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PG Reading C Lab Script pdf

1. eee eee eee 187 14 5 Queues FIFO Butters cee be ee a hee Pk ee ee ee oe eee Da ees 188 14 6 Managing FIFOs as Circular Buffers 2 oe ee 190 14 SUMMA Via di Bae ok BS hee sh he Ee Bo BR a oe BE St 192 Lists and Queues 1 193 iv Computer Programming Using C Revision 1 3 16 17 18 15 1 OVeEVICW ats 23 A BE ee a Oe ee oe es 193 15 2 Storing Arrays of Pointers ee 193 15 3 The Limitations of Arrays ee 195 15 4 Introducing Linked Distri cs Bo RE ae ae eed ed Ae dere eee age 195 15 5 Working with Linked Lists 6 2 en 198 15 6 A Linked List Example iste i baat A bgt Se ea ae See tae at a dede 199 15 7 SUMMA Y do sores AN oye Rh A E pes ast Se A ee ee ae ee 202 Lists and Queues 2 203 VOL OVeEVIOW ts ar2 2 E Pos amp de da Oe Ae AA A ees ea ee 203 16 2 The Limitations of a Single Linked List 2 0 0 0 0000000000200 203 16 3 Introducing Double Linked Lists aoaaa ee 205 16 4 Manipulating Double Linked Lists 2 0 2 ooo o 206 16 4 1 Adding into a Double Linked List o ooo ooo o 207 16 4 2 Removing from a Double Linked List o o ooo ooo 210 16 5 So When Are Linked Lists Useful ee 211 16 62 SUMMA 75 08 o A A e a O AAA a A a a ee 212 File Handling 213 VA COMETVIE Wa a aide ee A A AS Bu et es E A LE da 213 17 2 Getting Access to Files o ooo ooo e 213 17 3 Simple File Read and Wr
2. Have a look to see what other parts of your program you think would be better substituted for a define tag Good programming practice says that you should consider using define tags whenever you have a fixed value in your program that you might want to change at compilation time like the window size Exercise 4 4 Adding a define Directive Music Option Open the music program you have been working on which should be called music2 Add a program_change function call for each channel you are using The instrument number used should be defined as a define tag For example the tag PIANO might be defined to be replaced by the number 1 like this define PIANO 1 Once you have done this add one or more define directives like the following define FIRST_CHANNEL_INSTRUMENT PIANO You would then change the program_change function call to be program_change 1 FIRST_CHANNEL_INSTRUMENT Notice how you are using one define tag to define another This technique can be very useful in making your program easier to read understand and change Have a look to see what other parts of your program you think would be better substituted for a define tag Good programming practice says that you should consider using define tags whenever you have a fixed value in your program that you might want to change at compilation time like instruments maybe even the musical key 4 5 Using define Directiv
3. Exercise 6 8 Drawing a Target Create a function called draw_target which uses code based on the skeleton to draw a suitable target on the far right hand side of the graphics window Feel free to decide e how many areas your target will have e what scores the different areas will have e how big the different areas of the target will be Exercise 6 9 Giving the User a Score Now the user has a target to throw the object towards the computer should reward them with a score that corresponds with the position in which the projectile path ends Your program calculates the vertical position of the projectile at each horizontal location It should stop when the vertical location is not above ground level The horizontal position at which the projectile is no longer above ground level will determine the score When the projectile reaches ground level or below your program should assign the corresponding horizontal position to a variable You can then use that variable which will be an x coordinate to calculate where on the target the object fell You should then be able to use the values in the scores array to give the user a score for their throw 6 8 Music Option The improvisation program you have been working on has been limited to producing whole tone scales or random notes It has been difficult to produce other scales as the differences in pitch between notes in say a major scale are not easily calculat
4. e Compile lab1 c will compile the current file lab1 c to produce an object file e Build lab1 exe will do any compiling that needs to be done of any files in the whole project then it will link the files together to produce the executable lab1 exe e Rebuild All forces the compiler to re compile everything from scratch even if it thinks it is not necessary We will be using the Build item the most often Select this item now The output window will show the messages generated by the compiler It should look like this AA Configuration labi Win32 Debug Compiling labl c Linking labl exe 0 error s 0 varning Build Debug Find in Files 1 Find in Files 2 4 You can see that the IDE ran the compiler which produced an object file and the linker which produced an executable It also tells you that there were no problems during this process i e there were no errors and no warnings Errors and warnings occur when there are problems with the C source code e errors are when the source code is not written in proper C language syntax and the compiler doesn t understand the compiler will give an error message to try to help you to understand the problem e warnings are when the source code is written in valid C but the compiler thinks you might have made a mistake It may be that you have mistyped something or the fl
5. Raises one number to the power of another number double pow double x double y The pow function raises the first argument to the power of the second argument and returns the result i e x For example result pow 2 3 would assign the value 8 to the variable result pow is defined in math h Function Reference sin cos tan Trigonometric functions double sin double double cos double double tan double The sin cos and tan functions take a single argument of type double which is treated as an angle in radians 27 radians 360 Each function returns a double value e sin returns the sine of the angle e cos returns the cosine of the angle tan returns the tangent of the angle sin cos and tan are defined inmath h Function Reference asin acos atan Inverse Trigonometric functions double asin double double acos double double atan double The asin acos and atan functions take a single argument of type double In the case of asin and acos this value should be in the range 1 to 1 The return value of each of these functions is an angle in radians 27 radians 360 represented as a value of type double e asin x returns sin x which will be in the range 7 2 to 7 2 e acos x returns cos x which will be in the range 7 2 to 7 2 e asin x returns tan x which will be in the range 7 to 7 asin acos and atan are defin
6. e the way that your functions in different files interact along with information about any header files that you have created e documentation and justification for any changes that you have made to the design whilst doing the implementation Someone should be able to understand your source code and how it works by reading your design implementation report and the source code itself 8 5 7 Verification and Testing The Verification and Testing section of your report should aim to prove that your software functions correctly This means that it should always react appropriately to user input it should meet the speci fication that you set out after your analysis and it should satisfy the requirements that were originally given to you Testing software is a very complicated process A perfect testing process or reg me would test your software against all the possible inputs it could ever take in all the conditions it all the conditions it could ever be run making sure that the outputs are appropriate In all but the most simple of cases this is infeasible It would just take too long So most software testing is a compromise Revision 1 3 Computer Programming Using C 143 With your own testing you must decide and justify what testing is necessary to prove that your soft ware works You should also comment on how you think your testing regime compares to the ideal in which every part of your program is tested How much of your
7. include lt stdio h gt Revision 1 3 Computer Programming Using 215 int main void FILE xfile handle int number Ask the user for a number printf Please enter an integer number scanf d amp number Get access to the file by opening it x file handle fopen number txt w x Write a single number to the file fprintf file_handle Sd number We re done with the file close it x fclose file _ handle return 0 This simple program first obtains an integer number from the user It then opens the file number txt for writing The next line of code uses the fprintf function to write to the file The fprintf function works exactly like the printf function or the sprintf function The difference between the fprintf function and the print f function is that the fprintf function takes an extra first argument the handle of the file to write to For example the code fprintf file_handle Hello Outputs the text Hello to the file identified by the file handle file handle The line in the lab17 program fprintf file_handle d number Outputs the integer number held in the number variable to the file as text 216 Computer Programming Using C Revision 1 3 Function Reference fprintf Outputting to a file using printf like place holders ate IONE TIONIc Oaa ele aaneen Olene Onee ICING 33 6 e g fprintf file_handle S
8. typedef struct long_list_type student_type first student_type current list_type The main function has one of these structures to keep track of the first student in the list the first pointer This is done with the member variable first The member variable current is used to reference the student structure which is currently being displayed A pointer to this structure is passed to all of the list handling functions This allows them to update the first last and current pointers if they need to Exercise 15 3 Understanding the Linked List Example Read through the source code and make sure that you understand how the program works If you have problems understanding parts of the program try stepping though them by setting a breakpoint if necessary Exercise 15 4 Keeping Track of the Last Student in the List Change the definition of list_type in types h to add a last pointer you should call it last This will allow the program to keep track of the last student in the list as well as the first To make this pointer work you must add the following things e you should add to the list_init function to make sure the last pointer is initialised to NULL e the list_ada function must be changed to set the last pointer if the list was previously empty Fill in the 1ist last function so that it sets the current pointer to point to the last student in the list 202 Computer Programming U
9. Distance distance_to_tokyo If at some point in the future you wanted to make all the variables of type Distance more precise you could change the typedef statement to define Distance as a double rather than an int typedef double Distance In this way typedef statements can help make your program more readable by making your types more flexible and your type names more descriptive By creating a type called Distance you have quite a good idea about what variables of that type are going to store typedef statements are especially useful when dealing with structures which is why they are being introduced in this lab When we defined a structure for holding student details it was done likes this struct student_type char family_name 40 char given_name 40 int year_of_birth int course_code y This effectively defines a new type but to use this type we have to use the struct keyword as well You saw this in the lab11 program struct student_type student We can make this shorter and therefore easier to read and type by using a typedef First let s change the structure definition to rename the structure type name struct long_student_type char family_name 40 Revision 1 3 Computer Programming Using C 155 char given_name 40 int year_of_birth int course_code Ver The prefix long has been added because we are going to create a type name which can be used as shorthand and this is the lo
10. Each parameter has a name and a type Note that even if the types of subsequent parameters are the same they must still be specified explicitly Exercise 5 3 Investigating Function Types Alter the lab5 to use doubles instead of integer values You will need to think about the square function head the variables in main the placeholders used by the scanf and printf functions the message displayed to the user Compile and run your program to check that it works Make sure that it works with non integer values and that it still handles invalid text input correctly Revision 1 3 Computer Programming Using C 93 Exercise 5 4 Transferring Code into a Function You are now going to move the input code the while loop with all of its contents into a separate function You should call the function get double Make sure you can answer the following questions before you start typing e What should the return type of the function be e How many parameters does the function need e How do you want to be able to call the function You should end up with a program with four functions including main The main function should be quite short In general itis good programming practice to try and keep your main function short as it makes your program more readable Build and execute your program and test it several times to make sure that it works If you do not understand how to do this ask one of th
11. For example if we wish to add the number 1091 to the stack we would execute a line of code like the following buffer buffer_top 1091 The result of this is shown below ffer 7 s bustertop ffer 6 ffer 5 ffer 4 ffer 3 ffer 2 ffer 1l ffer 0 As we have now used another slot we must update the buf fer_top variable ffer 7 6 bustertop ffer 6 ffer 5 ffer 4 ffer 3 ffer 2 ffer 1l ffer 0 186 Computer Programming Using C Revision 1 3 The lab14 project implements a stack as an array When the program is running you have the option of adding or removing data items The current stack is shown on the left hand side A screen shot of the lab14 program running is shown below cr h clab lab14 Debug lab14 exe LIFO lt Stack gt Buffer Demo lt a gt Add a data item lt r Remove a data item lt q gt Quit lt Next free Choose an option 2 72 58 Bottom gt 926 SP Copy the lab14 project and open it in the IDE You will find that itis made up of three source files and two header files e lab14 c contains the main function and the add_item and remove_item functions which re spond to user requests to add and remove data items to from the buffer e display c contains the display buffer function which displays the current contents of the stack and the display menu function which displays the short user menu e
12. When we have finished using the memory we must tell the system that we no longer need it This allows the memory to be reused If we did not do this the system would use up memory every time we ran the program Allocating memory and forgetting to free it is called a memory leak int main void 0x89012345 0x12345678 my_array int my_array my_array malloc size free my_array return 0 Notice that when you free a block of memory the pointer that you used to access the memory in this case my array does not change However the memory that this pointer references no longer belongs to the program You must not attempt to access memory you have freed 178 Computer Programming Using C Revision 1 3 A call to the malloc function may not always succeed You are asking the system for a block of memory If it does not have enough memory to give you the malloc function will fail If it does the malloc function returns the special pointer value NULL If a pointer is NULL it indicates that the pointer is invalid If you try to use a NULL pointer your program will crash It is good practice to always check to see if malloc returned a NULL or a valid pointer You have just seen how the malloc and free functions are used to allocate and free up blocks of memory A call to the malloc function takes one argument the size of the block you wish to allocate C has a special operator called sizeof to help you calculate how much memory diffe
13. display h contains prototypes for the functions in display c e buffer c contains functions for handling the actual buffer The buffer_init initialises the buffer buffer_add does the work of adding an item to the buffer buf fer_remove is intended to do the work of removing an item from the buffer This function is not finished e buffer h contains prototypes for the functions in buffer c The lab14 program uses two functions that you have not seen before These are clrscr and gotoxy The clrscr function takes no arguments and clears all text from console text window The cursor is set to the top left hand side The gotoxy function takes two integer arguments which specify an x and y location in the console text window When the function is called the cursor is positioned at the specified location For example gotoxy 4 20 Sets the x location of the cursor to be 4 characters from the left of the screen and the y location of the cursor to be the 20th line from the top of the screen Revision 1 3 Computer Programming Using C 187 Function Reference clrscr Clears the Console Text Window woke elige oye s e g CITS CEAT The clrscr function clears the console text window of all text and sets the cursor location so that the next text to be displayed will appear in the top left hand corner of the window The clrscr function is defined in console_lib h Function Reference
14. display_welcome You will notice that no arguments are specified as part of this function call there is nothing between the parentheses The next part of the main function obtains an integer from the user using the scanf function It is more complicated than the way you have used scanf before because it checks to see whether the user actually entered a valid integer When the user types in a response the scanf checks what they typed against the placeholder it could either be e a valid integer in which case the scanf function has a return value of 1 e something else in which case the scanf function has a return value of zero This return is the number of placeholders that were matched with the text the user entered The return value is assigned to the variable called num_placeholders_matched But what happens if the user doesn t type in a valid integer To answer this question we must look at the way scanf works When you type in characters on the keyboard they get stored in a special variable in the stdio library This variable is called an input buffer TET achspace Eis Seeing A Bo Type on keyboard Hello Input Buffer H e TTo When you call scanf the first time the input buffer is empty because you haven t typed anything yet Because the buffer is empty scanf waits for you to type in characters and press Enter 88 Computer Programming Using C Revision 1 3 When you
15. larations To use the point structure a variable should be declared using type struct point scibucio Poline SCMmES ID ALME P The x and y parts of this variable can now be accessed using the dot operator For example some_point x 50 Copy the lab11 project and open it in the IDE This project is a very simple demonstration of how to use structures 154 Computer Programming Using C Revision 1 3 Exercise 11 1 Using Simple Structures Try building and executing the lab11 project Once you have run it and tried entering some details have a look at the source code Make sure you understand what is happening and how it is being achieved Add a member variable to the structure for favourite colour Add functionality to the program to allow the user to enter a favourite colour The program should also display the student s favourite colour when the other details are displayed 11 3 Defining New Types with typedef The typedef keyword allows you to define new types just like int and double The new types you define must be based on existing ones For example typedef int Distance declares a new type called Dist ance which is identical to int typedef statements are usually placed in the global scope of the program i e not inside any functions or in a header file so that the type may be used by lots of different functions The new type may be used in a variable declaration like this
16. 0 varning Debug h Find in Files 1h Find in Files2 4 From this window you can see the two major stages of compiling your programs this is a reminder from the first lab e compiling which produces an intermediate file called an object file for every source file in your project 74 Computer Programming Using C Revision 1 3 e linking which combines all of the object files with library files which contain the code for pre existing functions such as print to form an executable file your program We are going to look at the compiling stage in a little bit more depth What we have been called the compiling stage can actually be split into two major parts e the preprocessor which processes the text in your source file before it is passed on to e the compiler which does the work of translating your text written in C syntax into machine code object files The preprocessor takes as input a text file which contains the C program that you have written It produces as output another version of that text file still in text but expanded and altered slightly For example an important job that the preprocessor usually does is to remove all of your comments from the file so that the compiler never sees them The next few sections of this laboratory are going to focus on the preprocessor to understand what it does and to be able to use it to our advantage 4 3 Introducing the C Preprocessor Most of
17. Optionally an if statement can be followed by an else section which guards a second statement statement2 This second statement only exe cutes if the relational_expression evaluates to false You have already seen how to add an else section to an if statement You can produce a more com plicated and more useful structure by making the statement that the else part guards statement 2 in the above syntax box another if statement This allows you to connect if statements together for example if number_entered lt 5 else if number_entered gt 5 else if number_entered 5 You will need to understand how this works in order to be able to complete the next exercise Ask the one of the demonstrators if you need any help Exercise 2 3 Using Relational Operators Alter the lab2 program so that after it accepts the number from the user it prints either That number is less than or equal to zero or That number is greater than or equal to ten or That number is between one and nine appropriately If you don t know how to answer this question ask one of the demonstrators for help 2 4 Grouping Statements into Compound Statements gF Try adding a second printf statement to the final else condition of the program you have just written The code should look something a bit like this LE ses Revision 1 3 Computer Programming Using C 45 else if else PLINEE C 21037 print
18. lt 1 is true e testl lt 1 amp amp test2 gt 30 is true Make sure you understand these before you go on to the next exercise If you need help ask one of the demonstrators Exercise 2 5 Logical Operators From previous exercises you should have a program that takes a numeric input from the user and distinguishes between numbers that are less than or equal to zero numbers that are greater than or equal to ten and numbers in between In each case it should print a different response to the user from a number of print f statements Add to this program to allow the user to input two different numbers you should prompt them twice Use printf statements to show that the program can distinguish between the conditions e when either number is less than 0 e when both numbers are less than 0 e when the first number is greater than 10 and the other is not greater than ten The program should only need to display one of these messages you may need to structure your if else statements carefully to get it to do this 2 48 Computer Programming Using C 2 6 Dealing with Many Options Sometimes you may need to make a decision on a single variable where there are lots of possible options You could deal with this by stringing together lots and lots of if statements but C provides a special statement to deal with this situation called switch The switch statement allows you to specify a s which are the o
19. projects are compiled and linked You should remember from earlier labs that programs are built in two stages e compilation which produces an object file for each source file e linking which joins all of the object files together to make one executable The important part of this process is that the compiler only ever works on one source file at a time This is shown in the diagram below graphics1 c graph fun c y y Ju graphics1 obj graph_fun obj Se lt gt graphics1 exe In this example the graphics1 project is being built There two source files graphics1 c and graph fun c The compiler first works on the graphics1 c file and produces the intermediate file graphics1 obj It then works on the file graph_fun c and produces the intermediate file graph_fun obj The compiler has now finished its work The linker now runs It takes the intermediate files graphics1 obj and 122 Computer Programming Using C Revision 1 3 graph fun obj and combines them together to make the executable file graphics exe The files in your project will probably have different names but the principle is the same To make sure that you don t get compiler errors or warnings you must make sure that for each function that is used in one file and declared in another you must specify a prototype for that function So for example in the example above e say graph fun c
20. which turns a true into a false or a false into a true The not operator is an exclamation mark You may need to use parentheses brackets with the not operator to ensure that the operator is applied to the correct part of the expression Revision 1 3 Computer Programming Using C 47 Syntax Logical Operators relational_expression amp amp relational_expression relational_expression relational_expression relational_expression Logical operators allow relational expressions to be connected together to form larger relational expressions There are three logical operators which form expressions which may be evaluated to true or false depending on the truth value of the expressions they are connecting e and amp amp evaluates to true only if both the relational expressions it connects evaluate to true e or evaluates to true if both either or both of the relational expressions it connects evaluate to true e not evaluates to true only if the expression it is modifying evaluates to false So for example if we have two variables test 1 which is 5 and test 2 which is 21 then e testl lt 10 amp amp test2 gt 30 is false e testl lt 10 test2 gt 30 is true e testl lt 10 amp amp test2 gt 20 is true e testl lt 10 test2 gt 20 is true e testl lt 1 amp amp test2 gt 30 is false e testl lt 1 test2 gt 30 is false e test1l
21. 3 x Declare a character array to store the string in x char string_data 20 Ask the user for a string printf Enter a word scanf S19s string_data Show them the string printf The word you entered is s n string_data x Tell them what the first character was printf The first character of the word is c n string_data 0 return 0 You should see that the program is quite simple it uses a scanf statement to read in the string It then displays the string using printf and then displays just the first character using another printf statement The scanf and printf statements use a placeholder that you haven t seen before for handling strings s For example the printf statement uses the s placeholder to substitute the characters out of the string variable and into the string which is going to be displayed You will notice that the scanf statement also uses a s placeholder to read in a string However in the case of scanf a number appears between the percentage sign and the s character The number is the maximum number of characters to read into the string It ensures that the program does not try and put too many characters into the array When using an array with scanf you do not need to use the ampersand character amp before the variable name The reason for this is a little complicated and you will study it in more detail in laboratory 13 next term Function Re
22. 3 Computer Programming Using C 133 if the key was c or C clear the screen and reset the position to centre if the key was q or Q set leave to be 1 loop while leave is zero close the graphics window The detailed algorithm for the main can be described in pseudo code as follows function main call display_welcome function initialise the graphics window to WINDOW_SIZE_X WINDOW_STIZI set curr_x to be WINDOW_SIZE_X 2 set curr_y to be WINDOW_SIZE_Y 2 call reset specifying curr_x and curr_y set leave to be 0 begin loop call getch to get a key from the user put the result in key if key is zero then call getch again putting the result in key end if switch using key E K case up arrow key subtract MOVE_DISTANCE from curr_y case left arrow key subtract MOVE_DISTANCE from curr_x case down arrow key add MOVE_DISTANCE to curr_y case right arrow key add MOVE_DISTANCE to curr_x case E or er set curr_x to be WINDOW_SIZ set curr_y to be WINDOW_SIZ end switch if curr_x is greater than 640 set curr_x to be 640 else if curr_x is less than zero set curr_x to be zero end if if curr_y is greater than 480 set curr_y to be 480 else if curr_y is less than zero set curr_y to be zero end if switch using key case any arrow key draw a line to the new curr_x and curr_y position case E or Yo call reset specifying curr_x and curr_y case Q or g s
23. 61 case s or S set pitch to be 62 case e or set pitch to be 63 case d or D set pitch to be 64 case f or F set pitch to be 65 case t or T set pitch to be 66 case g or G set pitch to be 67 case y or Y set pitch to be 68 case h or H set pitch to be 69 case u or WU set pitch to be 70 case j or J set pitch to be 61 case k or K set pitch to be 72 case q or Q set pitch to be PITCH_QUIT any other case set pitch to be PITCH_INVALID end switch return from the function with pitch end function display_welcome 4 E This completes the design 8 4 3 Implementation You should now take the time to make sure that you understand how the design is proposing to solve the problem The way that the main function uses the special pitch values PITCH_INVALID and PITCH QUIT is quite complicated Have a think about how this translates into C Copy the lab8 project You should find that the lab8 c source file is completely empty This is ready gF for your own code Exercise 8 5 Implementing the Design Implement the KeyNote program according to the design You will need to choose appropriate C statements that match with the pseudo code You will also need to make sure that you include the correct header files 140 Computer Programming Using C Revision 1 3 Exercise 8 6 Chec
24. 9720 distance_to_airport 120 This statement is called an assignment It copies whatever is on the right hand side of the equals sign to whatever is on the left hand side In other words the variable on the left is assigned the value on the right The item on the left hand side must be a variable An assignment is very different to the way an equals sign is used in mathematics An equals sign in maths declares a relationship between the left and the right hand sides e g x y z in maths tells you that x y must be equivalent to z The equals sign in C copies information The first line of code above copies the value 9720 into the variable distance_to_tokyo This means you can write statements which make a lot of sense in C but no sense in maths such as someCounter someCounter 1 Which means that the variable someCounter will be one greater in value after this line than it was before Because you take the value of someCounter add one to it and copy the result back into someCounter The next few lines carry out some mathematical operations All the lines that do maths are also assign ments They carry out a calculation and assign the result to a variable For example the line time_to_drive distance_to_airport speed_of_car takes whatever the value of the variable distance_to_airport is it then divides is by whatever the value of the variable speed_of_car is and copies the result into the variable time_to_d
25. A formal approach to the development process helps to prevent errors A small error in an early stage of the process can grow to become a large problem in the finished program Such large problems tend to be very expensive and time consuming to fix The software engineering process is usually broken down into the following steps e understanding the problem so that a set of Requirements may be created This stage is often called Requirements Capture or Requirements Elicitation analysing the requirements to understand how the problem may be solved This stage is usually referred to as Requirements Analysis or just Analysis The aim is to gather information ready to produce a formal specification for what the software should do the creation of a formal Specification A specification is typically split into things that the software is required to do and things that are desirable for the software to do using the specification as the starting point for a software Design There are many approaches to designing software but the aim is always the same to decide exactly how the software will work and how it will be used before any actual programming takes place e the Implementation of the program In your case this would be done in the C programming language This is the only part of the process that actually involves programming The way in which the design is implemented is documented in an Implementation Report 130 Computer Programming Using
26. Drone Tones for Depth The next step is to add some depth to your piece by allowing one or more drone tones to play in the background You might like to change the tone that is used during the piece You could do this once or even at the beginning of each set of scales You might choose to play the tones on a different channel and instrument to the scales 3 6 4 Playing Until Told to Stop The kbhit function allows you to find out whether the user has pressed a key on the keyboard You use it like this int_variable kbhit If the int variable has the value 0 after this function call then no key has been pressed You can use the kbhit function to repeat a part of your program until a key is pressed For example the following do while loop will execute the statements inside it until a key is pressed do while kbhit 0 It is very important to note that because the kbhit function is called at the end of every loop to check if a key has been pressed this loop will always execute a whole number of times Function Reference kbhit Checks to see if a key has been pressed int_variable kbhit The kbhit function tells you whether a key has been pressed It will return the value 1 if a key has been pressed or the value 0 if no key has been pressed This value will be assigned to the int_variable if it is present The kbhit function does not wait for a key press You can retrieve a number identifying w
27. From this point on functions will be described using their prototype like this int getch void Rather than using the syntax type method used up to this point which has looked like this character getch 5 6 The Maths Function Library So far on this course you have been introduced to a number of different functions that are part of the C standard library This have been functions defined in stdio h and conio h You are now going to use some mathematical functions defined in math h You have already written your own function for squaring numbers math h defines a square root func tion called sqrt It also defines trigonometric functions sin cos tan inverse trigonometric func tions asin acos atan and many more You will find full documentation for all of the available mathematical functions in a book on C or on the internet Some suggestions for reading are given in Appendix B you will also have been given some suggestions for reading in the lectures This section introduces some useful maths functions that you may need during the rest of the course Function Reference sqrt Calculates the square root of a number double sqrt double The square root function takes one argument a value of type double and returns another double value which is equal to the square root of the argument sqrt is defined in math h 96 Computer Programming Using C Revision 1 3 Function Reference pow
28. Given Name Year of Birth Course Code Next Pointer 0x23456789 Given Name Year of Birth Course Code Next Pointer 0x34567890 Given Name Year of Birth Course Code Next Pointer 0x45678901 Given Name Year of Birth Course Code Next Pointer Family Name Family Name Family Name John 1986 610 0x23456789 Doe Jane 1985 600 0x34567890 Bloggs Fred 1982 606 0x45678901 Jones Francis 1974 636 NULL The last structure in the list does not need to reference anything but it does need to indicate that it is the last structure in the list To do this we may sure that the Next Pointer of the last structure in the list has the special value NULL As you may remember from lab 13 the value NULL indicates that a pointer is not valid The pointer that references the first structure in the list is usually known as the head pointer or the first pointer The member variable in each structure which references the next structure in the list is usually known as the next pointer 198 Computer Programming Using C Revision 1 3 15 5 Working with Linked Lists When a program using a linked list starts it will make sure that the first pointer is set to NULL students NULL This indicates that the list is empty NULL students To add the first item to the list we must go through the following steps e allocate the memory for the new item e set appropriate membe
29. RENATO ETA IS OA IF e POB ICL IFILL 2 JINE FILL 9 INTERLEAVE_FILL 3 TSLASH ETLE 10 WIDE_DOT_FILL 4 SLASH FIL lil CLOSE DOT IPI 5 BKSLASH FILL 12 USER_FILL 6 LTBKSLASH_FILL For colour_number you can use any of the names defined for the set color function see function box on page 29 The most common pattern and perhaps the most useful is SOLID_FILL setfillstyle is defined in graphics 1ib h 54 Computer Programming Using C Revision 1 3 Function Reference fLoodfill Fills an area with a coloured pattern floodfill x y boundary_colour The floodfi11 function begins filling the screen with colour working outwards in all directions from the location specified by the coordinates x y The fill spreads in all directions until it reaches a line of colour boundary_colour when it stops This colour serves as a perimeter for the fill The fill takes place in whatever the current colour is and whatever the current style is These are set by acall to the set fillstyle function setfillstyle SOLID_FILL RED ielevochesilil OO 100 W r will fill the screen with red start from location 100 100 and stopping wherever a white line is encountered floodfillis defined in graphics 1ib h Exercise 2 10 Using floodfill Add to your program to ensure the stick person s head is filled with the same colour as the colour used to draw the body You might like to try out different fil
30. Using C Revision 1 3 e The IDE window should look like this Microsoft isual C ES Edit View Insert Project Build Tools Window Help IICA CES eel2 c nar aj Jl a Opening a Project in the IDE To begin or continue work on a project you have copied you must open the project in the IDE each project is contained in a workspace e With the IDE open click on File Open Workspace Microsoft Yisual C l File Edit View Insert Proje l C Mew Ctri N E Open Ctri O Glose Open Workspace Save Workspace e You should now be viewing the contents of My Documents Revision 1 3 Computer Programming Using C 9 Open Workspace 2 xi Look in A My Documents y e E E corel user Files CyberLink exceed ini My eBooks My Music Files of type workspaces dsw mdp y Cancel A e Double click on the clab folder to view its contents Open Workspace 7 x Look in SY clab 7 e ck Ee lab File name NA A A Files of type Workspaces dsw mdp y Cancel JE h e Double click the folder of the project you want to open in this example we will be loading the project lab1 Open Workspace E x Look in ETI y e 1 e En abi File name lab1 dsw Files of type Workspaces dsw mdp y Cancel Y A e Select the workspace for the project This will be a file with the same name as the project in this exam
31. WINE is tard a ow aa do ee Seas T8 Music Opin merania a o amp dalek REG te oe eG ES E 1 8 1 A Simple Music Program 2 0 ee 1 8 2 Playing More than One Note at Once 1 2 0 0000000 eee eee 1 8 3 Changing the Instrument 2 0 oo WI SUMMA Va ASAS A O a ii TES 2 Conditional Statements The if and switch Statements 2 2 Getting Input from the User i aoe enan g e ee a a ea a ea 2 3 Making a Decision Conditional Statements 2 2 2c ee ees 2 4 Grouping Statements into Compound Statements 2 2 0 oo e 2 5 Making More Complex Decisions Logical Operators o o o oo ooo 2 6 Dealing with Many Options 2 0 E k ERAR BORTI E ees 2 7 Getting a Single Character from the User 2 2 ee ee es 2 8 Graphics Option sa ata Sth a a en ee a ee aye Se ee a 2 9 Music Options ir betes ged oth ean a a BS AN Bb oe Daten a aw Aes 2 1 0 SUMMARY ts ihe Carte alo toe oe Seva Ge oe hye ya aye terns UA a aes de EA lore a e 3 Repetition and Iteration do while and for dal COVE We le a a he d 3 2 Repeating Statements Many Times e 3 3 Repeating Statements and Counting 6 o a WOON TK W WwW WwW ii Computer Programming Using C Revision 1 3 3 4 Deciding What Kind of Loop to Use o o ooo o o eee eee 64 3 5 Graphics Option seis s aai Ee eae PEE 6 ale we A AA S 64 3 6 Music Optton e240 ays ete ab A a aE Be age a EG ee a 6
32. a return type like in the case of the square function or the get ch function this does not mean that you must assign the result to a variable You don t have to For example 92 Computer Programming Using C Revision 1 3 key getch calls the get ch function which waits for a key press and when the function returns it assigns the result the code for the key that was pressed to the key variable You could also call get ch like this getch In this case the get ch function is still called and it still returns a value but the compiler throws that value away because you have not assigned it to a variable In this case the get ch function will still wait for a key press and return the value of key that was pressed However that value will be discarded because no assignment was specified Syntax Function Definitions return_type function_name parameter_list or void A function definition declares the name of a function function_name and associates with it a return_t ype which may be void and a parameter_list which may also be specified as void Specifying the return_t ype as void indicates that the function will not be returning a value Spec ifying void in place of the parameter list indicates that the function should not be called with any arguments A parameter_list has the following syntax type name type name For example int paraml double param2 Wie ekcem ane pezei saline joeseeNnS
33. are no hard and fast rules as to what kind of loop you should use in a given situation Here are some guidelines to help you to make a decision when designing and coding your own programs You should refer back to this list in later labs whenever you are not sure what type of loop to use e In general the for loop tends to be the neatest and easiest to read loop when you have some kind of counter variable Even if the counter is not simply counting up it could be counting down or in steps of 2 etc The for loop is also an obvious choice when you know in advance how many times the loop should be executed e If your code does not neatly fit into a for loop you probably want a while loop If the condition at the top of the while loop is not met the first time the loop will not execute at all Quite often this behaviour is exactly what you want e Youshould use do while loop when you think a while loop is appropriate and you are certain that you always want the loop to execute at least once 3 5 Graphics Option We are going to add to your graphics1 project to allow your stick person to throw an object The graphical display will show the path of the object It should look something like this Windows BGI First we will have a brief look at the mathematics we need to describe the path of an object Once we have the maths we will write some C to carry out the required calculations and plot the results We will begin by as
34. are very similar to the reasons for using functions in the first place e using multiple files adds structure to your program and makes it easier to understand For exam ple you could collect all the functions that produce output on the screen into one file making it easier to find functions of a particular type e putting a set functions into a file allows you to use the same file in multiple projects If there are bugs in the functions in that file you only have to fix them once rather than having to change the code in every project it is used in In this lab you will learn how to split your source code into multiple files by placing different functions in each file Begin by opening the project that you have been using for your option work in the IDE So if you have been doing the graphics option you should open graphics1 or if you have been doing the music option you should open music2 These programs are getting quite complicated by now and probably contain a number of functions You are going to separate these functions into two files depending on their role in your program 120 Computer Programming Using C Revision 1 3 Exercise 7 1 Deciding on a File Structure Before you actually create any new files or change your program in any way you should decide how and why you will structure the files Decide how many files you want to use This should be more than one and no more than about four at the mo
35. channel 1 x The note will have a medium velocity volume velocity 64 x Start playing a middle C at moderate volume midi_note pitch channel velocity x Wait for 1 second so that we can hear the note playing pause 1000 x Turn the note off by setting its volume to 0 x midi_note pitch channel 0 return 0 We will go through this program a few lines at a time Make sure you understand it before continuing At the top of the source file after the initial comment is the line include midi_lib h This allows the compiler to understand the MIDI music functions This works in the same way as the include lt stdio h gt line you needed to put into your code to allow the compiler to understand the printf function The next few lines set the values of integer variables which will control the note that the computer plays pitch 60 channel 1 velocity 64 We will see what these numbers mean in a moment when we look at the midi_note function The next line starts the computer playing a sound it turns a note on midi_note pitch channel velocity The midi_note function is perhaps the most useful function you will use for creating sounds It is used to play a note of a certain pitch on a certain channel MIDI allows 16 different channels each of which can be set up to sound like a different instrument Each channel can have notes playing on it at the same time You can therefo
36. character code To find out what key was pressed then you should assign the result of the function call to an integer variable one of type int int_variable getch There are some special cases which relate to keys on your keyboard which are not straightforward letters The best example is the arrow keys In these cases when you call get ch and the user presses an arrow key it will return zero You will then need to call get ch a second time This time get ch will not wait for a key press It will return immediately with the value of an arrow key In case a user presses a non character key get ch should always be properly used as follows int_variable getch iit ime wariaole 0 int_variable getch You should see from this code that get ch is called twice if the value from the first get ch was zero In this case the value of the key can be tested to see if it matches one of many useful values including the arrow key values which are shown below Key Value 75 i 72 77 I 80 Enter 13 In some cases the get ch function may return the number 224 instead of zero to indicate that an extended key has been pressed It is usually good practice to check to see if a call to get ch returns either zero or 224 getch is defined in conio h and also graphics_lib h 52 Computer Programming Using C Revision 1 3 Exercise 2 7 Using getch and switch Adapt the lab2a program to use get ch instead of
37. colour names as for set color which are listed in the function box on page 29 setbkcolor is defined in graphics 1ib h Function Reference outtextxy Draws text in the graphics window void outtextxy int x int y text The outtextxy function places the text in graphics window at the location specified by x and y text should be enclosed in double quotes in the same way as with printf Unlike printf however you can t use placeholders with out text xy The text is drawn in the current colour For example outtextxy 100 250 Press Enter to Continue would display the text Press Enter to Continue starting at location 100 250 Important You will notice that the prototype given above for the outtextxy function does not have a type for the third argument text This is because we have not yet studied how to specify the type for variables containing text We will cover this in the next laboratory outtextxy is defined in graphics 1ib h Exercise 5 10 Using the New Graphics Functions Now is your opportunity to use the new graphics functions cleardevice setbkcolor and outtextxy to add to your graphics program You could e use cleardevice to clear the graphics window in between each of the user s throws instead of opening and closing the window e use outtextxy to display helpful text for the user e change the background colour to something other than black for the scene using setbkcolor and cleard
38. defines a function called show_welcome which is called by the main function in graphics1 c e for the compiler to know that the function exists in another file there must be a prototype for show_welcome in graphics1 c This situation is shown in the diagram below void show_welcome void int main void Function call matched hics1 show_ welcome with prototype graphicsl c Prototype matched with function void show_welcome void graph fun c Exercise 7 2 Declaring the Correct Prototypes You should now have created the files that you decided on and moved the parts of your source code to the relevant files Make sure that each source file you have created contains the prototypes of each of the functions it needs that are in other files It is standard practice to put a comment at the top of each file docu menting what the purpose of the functions in the file are Make sure you add a comment like this to the top of each file that you create Your program should now build and execute without warnings or errors 7 3 Creating Your Own Header Files To decide what prototypes are necessary you have to check your source file to find out what functions if any you use from other files When your source files are large it is easy to forget which functions are called Including prototypes which are not called will not generate an error or warning but it is misleading for anyone reading your source
39. determines the colour that is used for future graphics drawing operations The colour is set using the colour_number argument which is an integer from 0 to 15 You can just pass it a number but the graphics system defines some colour names to make it easier to use O BLACK 8 DARKGRAY 1 BLUE 9 LIGHTBLUE 2 GREEN 10 LIGHTGREEN SLOGAN 11 LIGHTCYAN 4 RED 12 IGHTRED 5 MAGENTA 13 LIGHTMAGENTA 6 BROWN 14 YELLOW 7 LIGHTGRAY 15 WHITE For example to set the drawing colour to yellow you could either write Seco ileal ara or setcolor YELLOW setcolor is defined in graphics_lib h The next line actually draws the circle on the screen circle x_position y_position 10 The circle has its centre at x_ position y position and has a radius of 10 pixels Function Reference circle Draws a circle in the graphics window circle xpos ypos radius The circle function draws a circle in the graphics window in the current colour The circle will have its centre point at the position specified by xpos and ypos which are coordinates from the top left corner of the graphics window in pixels It will have a radius as specified by radius in pixels For example clrcle 200 300 20 5 will draw a circle with its centre at 200 300 with a radius of 20 pixels circle is defined in graphics 1ib h The next line calls a function which waits for a
40. e Stacks are buffers where the item of data you get out is the last item of data you put in The next item of data you get out is the second to last item of data you put in and so on Just piling objects up into a stack A stack is also called a last in first out buffer or LIFO e Queues are buffers where the item of data you get out is the first item of data you put in The next item of data you get out was the second data item you put in and so on Just like a queue of people waiting to be served at say a bar A queue is also called a first in first out buffer or FIFO 184 Computer Programming Using C Revision 1 3 The lab will look at LIFOs first and then FIFOs Buffers are widely used but the most common uses are in situations where you will use them without knowing LIFO buffers are used by almost every microprocessor system whether complex like a PC or simple like a washing machine or a microwave You will learn more about this use of LIFO buffers in some of your other courses You have already seen the use of a FIFO buffer in lab 5 This keyboard input buffer which stores key presses before they are collected by function calls such as scanf and getch is a FIFO buffer FIFO buffers are used in many other situations and are perhaps the most widely used type of buffer All the buffer examples in this lab use integers as the data type There is no reason why this has to be the case The data items could be doubles chars arrays struct
41. enters to make sure it is valid If you don t understand how to do this ask one of the demonstrators for help 6 5 Strings A Special Kind of Array You have already used pieces of text many times in your C programs They have usually been in printf statements and have been enclosed in double quotation marks like this A piece of text like this is called a string because it is treated by the programming language as a string of characters The name string is just an abbreviation In C strings are treated as arrays of type char Each element in the array holds a single character For example we could declare an array to hold strings like this char some_string 8 Initialising a character array like this is quite easy for example char some_string 8 Hello When a character array is initialised like this each letter is stored in an element of the character array some_string Like this Revision 1 3 Computer Programming Using C 111 tring 0 string 1 tring 2 tring 3 string 4 tring 5 string 6 tring 7 You will notice that the element immediately after the last character in the string some_string 5 in this case contains a the character 0 that s a backslash character and a zero character not the letter o This is an escape sequence just like the special sequence for a new line n 0 is the escape sequence for the null character It is used to signal t
42. for each file that you open Once you have closed the file the file handle is no longer valid A file handle variable is declared like this FILE file handle To open a file you should use the fopen function This function requires two arguments both of which are strings the name of the file you want to open and the access mode you wish to have The access mode is to do with what kinds of operations you wish to carry out on the file Specifying w indicates that you wish to write to the file r specifies you wish to read and w specifies that you want to be able to both read and write For example the following line of code file_ handle fopen number txt w opens the file numbers txt for writing If the fopen function could not open your file for whatever reason the file handle in this case the file_handle variable is set to NULL When you are finished with the file you must close it again using the fclose function This function takes only one argument the file handle of the open file you wish to close fclose file_handle 214 Computer Programming Using C Revision 1 3 Function Reference fopen Opens a File FILE fopen charx filename char access_mode e g file handle fopen data txt w secret_file fopen important dat r temp_file fopen temporary tmp rw The fopen function attempts to open the file specified by the filename argument with the access mo
43. from the integer variable my_integer The amp oper ator is called the reference operator because it allows us to create a reference from a variable A reference pointer to the variable my_integer is created and assigned to the pointer variable ref_my_integer int main void 0x12345678 my integer int my integer int x ref_my integer 0x89012345 0x12345678 ref_my_integer H ref my integer amp my integer my integer 20 printf my integer is d n my_integer xref my integer 5 printf my integer is now d n my integer return 0 The next line assigns the value 20 to the variable my integer and then uses a call to the printf function to display its value int main void 0x12345678 20 my integer 0x89012345 0x12345678 ref my integer my_integer 20 printf my_integer is d n my_integer int my_integer int ref_my_integer ref_my_integer amp my_integer xref_my_integer 5 printf my integer is now d n my integer return 0 The next line uses the ref my_integer pointer variable with the operator The operator is called the dereference operator and tells the program that we are not talking about the pointer variable ref_my_integer by what ever it references in this case the my_integer variable Revision 1 3 Computer Programming Using C 167 int main void int my_integer int xref_my_integer ref my integer my integer my_integer 20 print
44. function on its own is called a prototype It should be exactly the same as the head of the function but with a semi colon at the end It should be placed outside of any other function For example a prototype for the square function would look like this int square int value Note the semicolon on the end of the line Because the compiler only needs to know the types of param eters in the parameter list their names don t really matter at this stage you can miss the names out like this int square int A prototype like this would usually be placed somewhere near the top of the file just after any include lines Revision 1 3 Computer Programming Using C 95 Exercise 5 6 Using Prototypes to Change the Order of Your Functions Declare prototypes for all of your functions except main Move the order of functions in your file so that main is above the other functions You might like to try and put the functions in some kind of logical order If you don t understand how to do this or if you are still getting errors or warnings when you try to build your code ask one of the demonstrators for help In the same way that a prototype is all the compiler needs to know about a function a prototype is also all the programmer needs to know about a function From this point on the laboratory scripts will use prototypes to define functions in function reference boxes Function Reference Change to Function Boxes
45. gotoxy Sets the Console Text Window Cursor Position VOICE coros slime po lime y E e g GoOroxy 5 110 2 The gotoxy function sets the cursor position in the console text window The cursor is set to the position specified by the function arguments x and y such that the next text to be displayed in the window appears at that location The x coordinate specifies the cursor position in character spaces from the left hand edge of the window The y coordinate specifies the cursor position in lines from the top of the window The top left cursor position is 1 1 The gotoxy function is defined in console_lib h Exercise 14 1 Working with LIFO Buffers Build and execute the lab14 project You should find that you can add data to the stack but not remove it This is because the buffer handling function buf fer_remove is not finished Read through the source code and make sure that you understand how the program works If you have problems understanding parts of the program try stepping though them by setting a break point if necessary When you feel that you understand the way that the program works complete the buffer_remove function so that data items can be removed from the stack 14 4 Buffer Problems Overflow and Underflow When you first looked at arrays in lab 6 it was mentioned that the array subscript the bit in square brackets after the array name could be any value When using arrays you must be care
46. have pressed enter it checks to see what is in the input buffer It then tries to interpret the characters in the input buffer in away that matches the placeholder you specified So for example Say you called scanf and you wanted an integer so you specified a placeholder of d cuernos El par pd i Zils A Ga Gas GG TE Type on keyboard 32 an T oa iz a Does it match a If the characters in the input buffer match the type that is required by the placeholder then it takes them out of the input buffer COPE rr El ttt ttt aii al FP a ETIT E Type on keyboard 32 E man A 2a m 32 matches d Input Buffer 3 2 Characters Removed The scanf call will then have a return value of 1 because it matched one placeholder If on the other hand the text does not match the placeholder scanf leaves the characters in the input buffer FLERE A a A Fl CIFTET ene Type on keyboard Hello ES de Hello doesn t match Sd o Input Buffer H e T T o Left in Buffer This is a problem If we call scanf again the first thing it will do is to check the input buffer It will find some text there already so it will not wait for the user to type in more text To get the next call to scanf to work properly we have to clear out or flush the input buffer We do that by calling the function f flush like this fflush stdin This tell
47. input e Specify a data table showing the name type and value range of each variable you will use There should be a logical flow through your design starting from the specifications and ending up at a full design for the program 8 5 5 Source Code Implementing the Design You will be expected to include the full source code to your software as part of a software report This is so that someone reading your report can understand how your software works and how they might add to it or change it Your code should be well commented Assume the reader of your code understands C Comments should explain why something is happening not what is happening They way you write code can also help a reader understand it Make sure that you use variables and programming statements in a logical way It helps if you choose logical names for variables and functions The way that you choose to lay out functions in your source files can heavily influence how logical your program seems to the reader It is often best to put the main function first in a C file with the same name as the program 8 5 6 Implementation Report Your source code should be supported by an Implementation Report This section tells the reader how the different elements of the design have been turned into C You should include in your implementation report e decisions you have taken when implementing the design such as what files you have used and what functions are in them
48. interested in If you do not understand anything about the program ask one of the demonstrators for help When you are sure that you understand how the program works change the source code to allow the program to accept up to 15 values rather than 10 Rebuild the program and test it to make sure that your changes have worked 108 Computer Programming Using C Revision 1 3 Exercise 6 2 Add a Standard Deviation Function The standard deviation of a sample of values measures how spread out the values are and may be calculated using the following formula 1x Se aye q Al o eae 61 Where e dis the standard deviation e x represents the ith data value e zis the mean of all of the data values e N is the number of data values The equation may also be written as the difference between the mean of the squared data values and square of the mean o 4 2 z 6 2 Add a function to lab6 called standard_deviation which takes the array of data values and the number of data values as arguments It should return the standard deviation You should add lines to the main function to call your new function and display the standard deviation on the screen Hints e Use equation 6 2 to calculate the standard deviation e Create a second array of the same maximum size as the data_values array i e 15 elements You should copy the original data items into this new array but square them
49. it can take more depending on how many variables you want to include e file_handle is a handle to a file previously opened with fopen which will be used as the source for all fscanf read operations e format_string is a string containing the place holders that fscanf will try to match input to fscanf uses the same place holder system as scanf As a reminder the most useful place holders are e d for integer int variables e Sc for single characters char e 1f real valued double variables The return value of scanf is the number of place holders that were successfully matched or the predefined constant EOF End Of File if there was a problem The fscanf function is defined in stdio h Exercise 17 2 Reading from a File Alter the lab17 program so that it reads a number back from the number txt file using fscanf and displays it to the user Remember to change the access mode in the fopen function call 17 4 Reading and Writing Many Lines to from a File The fprintf and fscanf operations are very powerful they are not just limited to writing a single number into a file and reading it back again There is no reason why you cannot place a fprintf function call like fprintf file_handle d n numbers index 218 Computer Programming Using C Revision 1 3 into a loop to write many consecutive number to a file from an array Notice the use of the new line escape sequence n t
50. letters like a b and c differently from uppercase letters like A B and C Build the executable again You shouldn t have any errors or warnings If you do ask the demonstrators for help Use the menu item Build Execute lab1 exe to execute the new program You should see a window containing the following text It takes 9 hours to get to Tokyo Press any key to continue Syntax Function Calls variable name argument argument To call a function you must first know its name and whether or not it needs any information when you call it Pieces of information that you give to a function when you call it are called arguments Ar guments are enclosed in a set of parentheses brackets and are separated by commas For example the function call prince Wie teles Sel laoui s o CSE lo Tokyon las Lo EOS p calls the printf function and passes two arguments The first argument is It takes d hours to get to Tokyo n and the second argument is time_to_tokyo Some functions give or return a result after they have been called We will meet some examples of these types of functions in later labs 24 Computer Programming Using C Revision 1 3 Function Reference printf Displays text on the screen printf format string data_item e g primer Mello Wortal yat q primei Wise che value o sua ine variables eya am Cwe printf Display the value o
51. limit When the user has finished entering the information draw the lines on the graphics window and wait for a key press You might like to add a feature to allow the user to edit the details of the lines that they have already entered so that they may correct mistakes A 2D coordinate is always made up of both x and y portions It would make sense to define a structure to hold coordinates or points in a 2D space typedef struct long_point_type int x y point_type Exercise 11 6 Nesting Structures Add the type definition for point_type to your program Change the definition of line_type so that the start and end location of the lines are specified as points You will end up with a structure inside a structure Exercise 11 7 Implementing Simple Vector Graphics Capability How do you think you could use one type of structure to define a range of shapes like lines squares circles triangles etc What things do they have in common What special items of information might you need for some of them How could you make a single drawing function draw all of the shapes Can you include flood fill information Try implementing a few of your ideas You will need to change your structure type definition the user input code and the drawing routine 158 Computer Programming Using C Revision 1 3 11 6 Music Option In this laboratory you will use structures to create a simple sequencer The s
52. linked into the list at all AAA m First Pointer ee NULL gt The new structure must be set so that its next pointer references the same thing as the first pointer and its previous pointer is set to NULL First Pointer NULL NULL The previous pointer of the structure which is currently first on the list must be set to reference the new structure 208 Computer Programming Using C Revision 1 3 First Pointer ra J n NULL Finally the first pointer must be set to reference the new structure _ First Pointer Pointer wth an 7 esco NULL The structure has been successfully added to the head of the list Adding to the Foot of the List Adding to the foot of a list is very similar to adding to the head of the list Rather than using the first pointer the last pointer is used The steps are you can compare these with the steps for adding to the head of the list e The new structure must be set so that its previous pointer references the same things as the last pointer and its next pointer is set to NULL e The next pointer of the structure which is currently last on the list must be set to reference the new structure e Finally the last pointer must be set to reference the new structure The completed operation results in the following situation AA oi _ Last Pointer Pointer lt esco gt NULL Add
53. list c source file in the lab15 project add a function to find the previous structure in the linked list It should have the following prototype student_type find previous student_type student The function takes a single argument student which should reference a structure in the linked list The function should return a reference to the structure that comes before student in the list Use the find previous function to implement the list previous function This should allow the user to move both forwards and backwards in the list using the arrow keys Exercise 16 2 Removing the Current Item At the moment the 1ist_remove function always removes the first item from the list Using the find previous function that you wrote in Exercise 16 1 change the 1ist remove function so that it always removes the current item from the list There are three situations to think about depending on where the structure is in the list What happens if the structure is e in the middle of the list e at the beginning of the list e atthe end of the list Revision 1 3 Computer Programming Using C 205 16 3 Introducing Double Linked Lists In many situations finding the previous structure in a linked list is essential The method that you used to do this is very inefficient but unavoidable if the list is only single linked A much more efficient way to solve this problem is to introduce another pointer into every struct
54. more difficult to set up and manage Great care must be taken to ensure that all pointers reference valid memory 16 4 Manipulating Double Linked Lists In a moment you will have to write some code to manage a double linked list Before this we will look at the key steps of the processes for adding and removing structures into a double linked list For both adding and removing operations there are four different situations to consider These are to do with the position in the list that structure will have in the case of adding or has in the case of removing The structure could be e first in the list e last in the list e somewhere in the middle e the only structure in the list this is a bit like being both first and last These situations are shown in the diagram below Revision 1 3 Computer Programming Using C 207 Structure Structure Structure Structure Structure E Teo Gun Structure Structure Structure First in the List Last in the List Middle of the List Only Item in the List This section will examine first adding and then removing Each operation will consider these four cases 16 4 1 Adding into a Double Linked List This section will look at the steps involved in adding a structure to a double linked list We will examine each of the four different situations under which this can occur in turn Adding to the Head of the List To begin with the new structure shown below shaded is not
55. operations are then carried out mean and standard deviation At the moment the memory in the array is statically allocated The number of data items the user can entered is therefore fixed when the program is compiled Change the lab6 program so that the user is asked how many data items they wish to enter at the beginning You should then use malloc to dynamically allocate the data array You can put a maximum limit of the number that the user enters if you want Remember to free the memory before the program ends 180 Computer Programming Using C Revision 1 3 Exercise 13 5 Strings and Memory Allocation In a similar way to Exercise 13 4 change the lab6b program so that the user can decide how long a word they wish to be able to enter You will need to be careful in how the scanf function call is constructed 13 5 Dynamic Memory Allocation for Structures Dynamically allocating memory for structures is very similar to allocating memory for arrays The structure name is used with the sizeof operator to calculate the size of the block of memory required For example to allocate a block of memory for one student type structure you would call malloc in the following way student malloc sizeof student_type Allocating memory for an array of structures is similar For example student_array malloc sizeof student_type 20 As you can see this follows the same pattern as allocating memory for
56. option is a different value of the variable specified at the start of the statement Each possible value of interest is described using a case clause A case clause has the following syntax case value A switch statement finds the first case that matches and continues to execute from that point onwards It will even continue into the next case To stop it executing at the end of the code for each case it is common to include a break statement The break statement stops any more of the switch statement from executing A case clause with a break statement looks like this case value break A default clause is like a case clause except that it matches anything This is commonly used at the end after all the case clauses to match anything that hasn t already been matched Because the default clause goes last it does not need a break statement Exercise 2 6 Flow of Execution in switch Statements Try using the debugger to step through the switch statement in the lab2a example Watch where the flow of execution goes What do you think will happen if you remove some of the break state ments When you have finished stepping through remove some of the break statements rebuild the project and try stepping through it again Does it do what you expected If you do not understand the program s behaviour ask one of the demonstrators 2 7 Getting a Single Character from the User The programs in this laboratory h
57. remov ing items from the queue Providing the queue is not empty the buffer_head variable tells us where 190 Computer Programming Using C Revision 1 3 the next data item is that we may remove In this case buf fer_head is 0 so we remove the data item 926 ffer 7 1 buffer_head 5 buffer_foot ffer 4 ffer 3 ffer 2 ffer 1 ffer 0 Notice that the buffer_head variable has changed to indicate where the new head of the queue is Exercise 14 3 Implementing a FIFO Buffer Change the lab14 example so that it uses a queue to store data instead of a stack You will need to add a variable to indicate the foot or bottom of the queue You will also need to change the buffer init buffer_add and buffer_remove functions 14 6 Managing FIFOs as Circular Buffers There is a major problem with the FIFO buffer implemented in an array as discussed in the previous section The problem occurs when the buffer has been filled and then emptied For example say that we add seven items to the buffer f o buffer_head ffer 6 buffer foot ffer 5 ffer 4 ffer 3 ffer 2 ffer 1 Now we will remove all of those seven items Revision 1 3 Computer Programming Using C 191 fFfer 7 buffer_head ffer 6 buffer_foot ffer 5 ffer 4 ffer 3 ffer 1 ffer 0 Notice that the array is completely empty and both the buffer_head and buffer_foot variables are 7 Des
58. s for strings char These are the same as for printf The return value of sprintf is an integer which specifies how many characters were written into the string variable array not including the null termination The sprintf function is defined in stdio h Revision 1 3 Computer Programming Using 115 Exercise 6 7 Using sprintf Add to the main function in lab6b to prompt the user for an integer number Use the sprintf function to create a string version of the integer in a character array you could re use one of the arrays you already have if it is big enough Determine the length of the string it produces in two ways e use your string_length function e use the return value from the sprintf function call Display both answers and make sure that they are the same If you don t understand how to do this ask one of the demonstrators for help There is a library that is part of the C standard library which contains a number of functions especially designed for handling strings All the functions are defined in string h If you want to find out more about these functions you should look in a book on C or consult documentation on the internet see Appendix B 6 7 Graphics Option Open your graphics1 project You will be adding even more functionality to it now By the end of this session it should reach the stage where you can play it as a simple game Your graphics program i
59. scanf The program should prompt the user for a single letter which is the first letter of a month The program should then display the months that begin with that letter You should use a switch statement for this The program should not care whether you use upper or lower case for example pressing either F or f should result in the program displaying February Hint You could use multiple case clauses to handle the upper and lower case letters For example case f case F break If you do not understand how to do this ask one of the demonstrators for help 2 8 Graphics Option We are going to alter the graphics program you were working on in the last laboratory to incorporate some of the new techniques you have just learned Close any project you have open at the moment and open the graphics1 project you were working on Your code from last lab should draw a stick person on the screen You are going to add to this code so that the user can decide the position of the stick person and the colour that it is drawn in Exercise 2 8 Adding User Control of Position to the Stick Person When your program starts the user should be able to type in a number which specifies the horizontal location of the stick person on the screen The user should be able to choose any location in the left half of the screen You should use an if statement to check that the number is sensible i e the user should not be abl
60. simple examples and then asks you to write a recursive program to search and array 18 2 Sorting Data Using a Bubble Sort You have been taught about bubble sorts in your lectures A bubble sort is a simple sorting technique which ensures a list of data items is sorted simply by comparing items a pair at a time The program determines whether the items are in order if there are not the items must be swapped over in the list Exercise 18 1 Sorting a Collection of Numbers Open the lab17a project that you worked on in lab 17 This program should read in a list of num bers from a file into a dynamically allocated array You should also have a file called unsorted txt which you created in lab 17 Alter the lab17a program so that it reads the numbers from unsorted txt You should write a function called sort which the program should call to sort the contents of the array The sort func tion should use a bubble sort technique Once the sort function has sorted the array of numbers your program should write the numbers into a file called sorted txt When you have executed your program open the sorted txt file and check that the numbers are in order Determining the order of numbers is fairly easy you can use the mathematical greater than gt and less than lt operations Comparing strings is more difficult Fortunately there are some standard C functions to do this for you The most useful string comparison fun
61. standard C types such as int and double Exercise 13 6 Structures and Memory Allocation If you have been following the graphics option open the graphics3 project if you have been following the music option open the music3 project These projects currently use a statically allocated array of structures Alter the program so that the array memory is dynamically allocated and freed Exercise 13 7 Reallocating Memory If the user of your graphics2 music3 program wanted to a a line note whilst the program was running how would you accommodate this it would require more memory to be allocated If the user removed a line note could you free memory up Have a go at implementing this into your program If the user is adding removing lines notes continuously allocating and freeing memory can make your program slow How could you make this process more efficient 13 6 Summary This laboratory re examined arrays and strings to show their close relationship with pointers You should now know that an array is simple a block of memory allocated by the compiler which is refer enced by a pointer Memory that is allocated by the compiler is called statically allocated memory Now that you have finished this lab you should know how to dynamically allocate memory using the malloc function call You should know that all dynamically allocated memory should be deallocated using the free function call Revisi
62. the condition that is checked to determine whether the loop should continue relat ional_expression is checked at the bottom of the loop rather than the top This means that the statement inside the loop will always execute at least once As in the case of the while loop it is common to replace statement and its semicolon with a compound statement Exercise 3 2 Using do while for Validation In the last laboratory you used if statements for user input validation i e checking that user input was valid If the user entered an invalid number your program simply ended It would be better if it told the user that the number was invalid Edit the code you have produced in the first exercise of this lab to prevent the user typing in a number greater than 100 or less than 1 If the user enters an invalid number the program should tell them why the number they entered was not accepted It should then ask them for a number again It should repeat the process of asking for a number until the user gives a valid input You should find that a do while loop is very useful for this purpose 60 Computer Programming Using C Revision 1 3 3 3 Repeating Statements and Counting There are many occasions when it is useful to have a loop which is controlled by a variable which counts the number of loops or iterations The for loop exists in C for this purpose The code below is from the project lab3a If you open the proje
63. the queue will be the first out of it this gives the queue its name a first in first out buffer A FIFO buffer can be based on an array in much the same way as a LIFO buffer Except now we must keep track of two points in the array the head of the queue and the foot end of the queue To under stand how a FIFO is managed in an array we will use a box diagram again The array name buffer is used again The buffer_head variable indicates the element containing the next data element to take out of the queue i e the next person to be served The buffer_foot variable indicates the next free slot in the array To begin with the buffer is empty Revision 1 3 Computer Programming Using C 189 f buffer_head buffer_foot Notice that both buffer_head and buffer_foot are zero This indicates that there is no data between the head and foot of the queue i e the queue is empty The next diagram shows that the data item 926 has been added to the queue buffer _head ffer 6 buffer_foot The buffer _foot variable has changed to indicate the next free element in the array Notice that the buffer_head has not changed because we have not removed any data items from the queue The next diagram shows that we have added the data items 58 72 2 and 86 to the queue buffer_head ffer 6 buffer_foot These diagrams have shown what happens when data items are added to the queue what about
64. this program The main function and another function called change Exercise 12 1 Investigating Function Parameters Before you try running the program look at it carefully Decide exactly what you think it will do What will it display on the screen Try running the program Does it do what you thought it would Do you understand why it operates in the way it does You should remember some important facts about functions from lab 5 e parameters the part in parentheses after the function name are just like variables e all variables and parameters that are declared in a function are only accessible inside that func tion e when a function is called it is common to specify some arguments in brackets after the function name e the values of these arguments are copied into the function parameter variables These points mean that if a parameter is changed inside a function the value of the variable that was used as an argument is not affected To emphasis this point let s look at how the simple program from the lab12 project works To begin with a value is assigned to the variable j This is shown below void change int 1 i 20 int main void int 5 j J 5 Copies the value 5 into variable 3 change j return 0 When the function is called the variable j is specified as an argument Its value is copied into the change function s parameter i see the diagram below Revision 1 3 Comput
65. to try again S not an integer while num_placeholders_matched lt 1 Revision 1 3 Computer Programming Using C 127 You can move a block of code to the left by highlighting it and holding down the Shift key when you press Tab Exercise 7 5 Cleaning Up Your Code This is the last time you will work on the program that you have been developing as part of your option You will find the ideas that you have worked on and the code you have written very useful in later laboratories and in your assignments To make sure your code is easy to understand you should e make sure you have commented your code thoroughly If you are unsure ask a friend to have a look at your code and see if they can understand what it does and how it works e make sure your indentation is correct and consistent If you are unsure about this check with one of the demonstrators There are no hard and fast rules for how to lay out and comment your source code in C although there is some generally accepted good practice With things like indentation it is most important that you are consistent across all of the source code in your project 7 6 Summary Now that you have finished this laboratory you should have either a music or graphics project that is split into multiple files in a logical way It should use header files protected by sentries to allow easy use and reuse of the code your have written You should understand the re
66. understand how to use them to debug your pro grams Finally you should have seen where to find the executable file that corresponds to each of the programs you have written 84 Computer Programming Using C Revision 1 3 Laboratory 5 Functions 5 1 Overview This laboratory will give you the capability to create your own functions and help you better under stand how existing functions are defined and called You will learn about e how to define functions of your own e how to specify parameters so that you can pass values to your own functions e how to allow your functions to return a value back to the place where they were called from e how and most importantly why you should use functions to split up your programs You will also be introduced to the f flush function which you will use to make sure that scan f handles user input better Some standard C mathematical functions are introduced which you might find useful in your own programs In the graphics and music options you will make use of functions to make your programs more readable and more powerful In the graphics option you will add the capability for the user to choose the launch angle for the object In the music option you will be introduced to the random_number program which you will use to try and create a program which improvises 5 2 Creating New Functions In most of the example programs you have seen and created so far you have used functions a gre
67. using print f like placeholders noaua aaa 114 mall e Memory Allocation eaa iraa aa SE A a ed ie oe 178 free Memory Deallocation ee 179 clrscr Clears the Console Text Window ee 187 gotoxy Sets the Console Text Window Cursor Position 0 0 00 eee 187 fopen Opensia Pile ot a A AL bid Led 214 felos Closes an Open File iia a ee A A A Rd A da 214 fprintf Outputting to a file using print f like placeholders 216 fscanf Performs a scanf like read from a file 217 random_number Generates a random number 218 strcmp strompi String Comparison 222 Syntax Reference DOME Syntax aga ha tho BN e A A eres oa a arias 2 COMMENTS Hiis es ee e a SE Bint IT OS il Se RO AA eek G 16 Variable Declarations o o ooo ee 17 Mathematical Operators sie trenean nae ep ke e E dre 18 Function Calls aii a a tae be ee Ba GO ee Pe A aun ee a Oe Be hee ee cas he ad 23 Relational Operators and Expressions ee 43 TE Statements ir a ee Senda Mee Refs use ana SVR Basen oP ae a eh aes oe ES a din BE de Ge ee es 44 Compound Statements sa sia ee a ee PS ek ee a ae Pu dts Gok Bak ws ROE EE 46 Logica Operators 25 ae ue bet rd Owe Ae Re PES Gabi a Ree ees 47 Switichstatements a a Va eh A a A a A o N aa 50 The while Loops at esi a A AA A AEE A il dah A a E 58 Thedo while Structure sl in a a A a a 59 Shorthand Operators ps 4 las ri a
68. way of grouping statements together to replace a single statement with many statements Any statement like this statement can be replaced by lots of statements like this statementl statement2 This is useful for making the if or else clauses of an if statement guard multiple statements 2 5 Making More Complex Decisions Logical Operators Student x wants to go to the bar which is only open after 7 00pm but she will only go if she has some money left We could try and code this decision in C it might look a bit like this if time gt 19 00 and bank_balance gt cost_of_one_drink go_to_bar finish_c_assignment else finish_c_assignment Please note this is not real C This kind of more complicated decision is common in everyday life To handle this kind of thing in programming code requires us to combine several decisions to form one complex decision The relational expressions we have looked at so far make a single decision on the basis of a comparison between two values which could be variables Quite often we need to be able to combine comparisons together with an and or an or These operations combine expressions which can already be evaluated to the logical values true or false in C they are known as logical operators In C an and is represented by the symbol amp amp an ampersand twice and an or is represented by a vertical bar twice There is an extra logical operator for not
69. which are explicitly intended for creating graphics easily on Windows This set of functions is an example of a software library The graphics library functions create a separate window to draw in Graphics are displayed in the graphics window by colouring the tiny dots that make up the display These tiny dots are called pixels Using the graphics functions you can control the colour of any pixel inside the graphics window Each pixel in the window has a location which can be described using an x and y coordinate much like on a graph The difference from most graphs is that the origin of the x and y axes is in the top left of the window 0 0 x axis y axis M You will be able to choose the size of the graphics window up to the size of the screen 1 7 1 A Simple Graphics Program If you have a project open at the moment the first thing you must do is close it Select File Close Workspace to do this You should then take a copy of the project graphics1 and open it in the IDE Check back to the Before You Begin section if you cannot remember how to do this The graphics1 program behaves quite simply at the moment It displays the graphics window which has a black background and draws a red circle on it When a key on the keyboard is pressed the window closes Try building and executing graphics1 The source code for graphics1 c is shown below A program to demonstrate si
70. your software did You may find it helpful if you number the points in your specification so that you can refer to them in later stages of your report 8 5 4 Design As you will have seen in this laboratory your design is where you make all the major decisions about how your program will work All these decisions should be made before you begin writing source code because you have a far better understanding of how the different pieces of your program fit together at the design stage A good design will be very detailed and should leave very few decisions to the programmer who im plements the design If you gave your design to someone else to code as well as yourself a user should not be able to tell the difference between the two versions No design decision should appear arbitrary they should all be linked to the points in your specification Here are some guidelines for things that you should include in your design 142 Computer Programming Using C Revision 1 3 e Describe your user interface in detail including exact coordinates of all lines on the graphics screen if appropriate exact wording of text the user will see and how when and where this will appear e Describe all acceptable user input and when it should be accepted by the program e Include a detailed structure diagram showing data flow between functions or parts of your pro gram e Give a description of all algorithms used including how you will validate user
71. 5 65 MB GE Local intranet e From the menu select File New Folder This will create a new folder on your home drive The folder will be called New Folder 2 My Documents File Edit View Favorites Tools Help Create Shortcut E Shortcut eis amp S Briefcase we POS Microsoft Word Document laa Limdep Command File la Limdep Project File Microsoft Access Application E Microsoft PowerPoint Presentation EJ Microsoft Publisher Publication Close Select an item to view Stores and manages See also E Quattro Pro 9 Notebook My Network Places a SAS PROGRAM 701 i Meamuri a Corel Presentations 9 Show Text Document D Wave Sound Ka WordPerfect 9 Document Corel Presentations 9 Drawing Microsoft Excel Worksheet CO PowerArchiver ZIP File e Type to rename the folder call it clab This is where you will keep all your projects for the C laboratory course Copying a Project Each of the labs in the course will use one or more projects that have already been created for you They are stored on the N drive but they must be copied into your clab folder before you can use them This will need doing each time you want to begin work on a new project 6 Computer Programming Using C Revision 1 3 Double click on the My Computer icon on your desktop My Computer e A window like the following should appear My Computer File Edi
72. 8 36 1 Simple Scales 30 raid daa gob da aa eet Re ETEO oe Berd E 68 3 6 2 Whole Tone Scales 2 ee 69 3 6 3 Adding to Your Whole Tone Scale Piece 2 2 ee ee ee 69 3 6 4 Playing Until Told to Stop 2 0 0 0 0 00000 eo 70 A gh eas pas ec ce ek tie ea Rah aoa Biel ohne oP Syd We a Gert 71 The C Preprocessor and Useful Debugging Techniques 73 AT Overview a A Reng deed PS E it Bee ee Bs AAA Sok ct A 73 4 2 StagesofCompilation ee 73 4 3 Introducing the C Preprocessor 2 eee 74 4 4 Using the Preprocessor for Text Substitution 0 0 0 0 00 0000000045 75 4 5 Using define Directives for Conditional Compilation o 78 4 6 Using Breakpoints for Debugging 2 2 ee 80 4 7 Locating the Programs You Have Written 2 2 ee 82 AS Summary lio 44d dd la a gnats a us Bae whe oa 83 Functions 85 Bil SOVERVICW A sii gad uk ot AE o AE Be oes ald be dp a ee td Be he ia 85 5 2 Creating New Functions sss aes sar aa p ek Go e Ree iin a ag aE oO LG 85 5 3 Anatomy of a FUnction se sa asis ne ta ia es 90 5 4 Functions Why Bother a A oa oe Se ae a be 93 5 5 Positioning Functions in a File 2 0 ee ee 94 5 6 The Maths Function Library o 95 5 7 Graphics Option sene s noaea u aa Se Oe ele a Gt dee we ee ea eS 97 5 7 1 Creating More Manageable Code 2 2 2 ee 97 5 7 2 Allowing Control of the Launch Angle 2 2 0 ee ee 97 5 7 3 Making Your Program More V
73. B w N e OM Al BH wN NI DM G Aj Go Copy the lab6a project and open it in the IDE lab6a is intended to be a program which informs the user of the distance between a small selection of major world cities However at the moment the program isn t finished The best way for the program to work out the distance between cities is to look it up in a table ie a two dimensional array You will need to create and initialise a suitable array to get the program to work You should initialise it with data from the table below The distances are in miles 110 Computer Programming Using C Revision 1 3 Cape Town Hong Kong London New York Rio de Janeiro Tokyo Cape Town 0 7 375 6 012 7 764 3 773 9 156 Hong Kong 7 375 0 5 982 8 054 11 021 1 794 London 6 012 5 982 0 3 458 5 766 5 940 New York 7 764 8 054 3 458 0 4 817 6 740 Rio de Janeiro 3 773 11 021 5 766 4 817 0 11 533 Tokyo 9 156 1 794 5 940 6 740 11 533 0 Exercise 6 3 Using an Initialised Two Dimensional Array Add a two dimensional array to the lab6a program and initialise it with the data shown in the table You can then use the indices that the user enters to look up the correct distance Some things to look out for e Remember that array subscripts are indexed from zero e Using a subscript that is beyond the range of the array can cause big problems Validate the data that the user
74. Build Start Debug Step Into g Build Tools Window Help 3 compile lab1 c Ctrl F7 Build lab1 exe F7 c 3 Rebuild All Batch Build Clean trate simple mathenat atory 1 Start Debug ES Debugger Remote Connection Y Step Into 1 Execute lab1 exe ctrl4fs CF Runto Cursor Ctrl F10 Attach to Process Set Active Configuration Configurations Profile iables for the calcul yo distance_to_airpo speed_of_car ime_to_drive time_to_ Your program will begin executing and will pause just before it reaches the first line The editor will show where it is up to with a small yellow arrow The main functicd XX int maln vold G Declare some int distance ti int peed_of p SA You can now step through your code a line at a time by using the Step Over item on the Debug gF menu which will have appeared once you started the program running 22 Computer Programming Using C Revision 1 3 El Go FS E restart Ctrl Shift F5 gk stop Debugging Shift F5 Ei Break Apply Code Changes AH FLO Fil Shift F11 PS H Run to Cursor CtrH F10 Step Into Specific Function vi t Eb Exceptions 1 El Threads d Modules S gt Show Next Statement Alt Num ES QuickWatch Shift F9 ama PAA You can also use the F10 key on your keyboard This will move the yellow arrow d
75. C Revision 1 3 e the software that has been produced must be carefully tested against the original specification and its functionality verified against the original requirements There are a number of ways to approach the Testing and Verification of software Usually more than one method is used to improve confidence in the correct operation of the program e before the software is passed on to a user or the original customer or client the operation of the program is documented in a User Manual An important part of the software engineering process is the documentation of each stage In the list above the words in bold indicate the names of each section of a typical software report A high quality of documentation is essential when software is being developed by a team of engineers rather than a single programmer Section 8 5 is a reference guide for software report writing giving you some tips for producing your own programs and reporting on the development process Rather than spend a lot of time in this lab doing paper work you will be learning about program design by using a design which has already been written This lab script will give you the specification and design for a piece of software assuming that the requirements and analysis have already been done They are not given here You will have to implement the software design you have been given Doing this will help you understand what is necessary in a good software design This s
76. It will have an icon a bit like this graphics 1 This example is for the graphics1 project This is the executable that was produced when you built the graphics1 or music2 project If you double click on it the program will run Try it The other files in this folder are intermediate files including the object files which were produced after the compilation stage and used by the linker to produce your executable Exercise 4 8 Running Your Programs from Executables Prove that your some of your other programs can be executed this way by finding their executable files and double clicking on them It is important to note that if you were to give your program to someone else to try out this is the only file they would need This executable file is exactly the same type of file that executes when you run any program on your computer You could copy this file onto any medium like a floppy disk or a CD or even make it available over the internet Anyone with access to just this file could run your program Revision 1 3 Computer Programming Using C 83 4 8 Summary Now that you have finished this laboratory you should understand the basic functions of the C prepro cessor including the include define if and endif directives You should be able to use define directives both on their own and in combination with if and endif directives for debugging You should have seen what a breakpoint does and
77. Keep track of the number of items we have here x int num_data_values x Some other useful variables x int curr_data_value done double mean_height Set initial conditions num_data_values 0 done 0 Display message to user x welcome_message x Loop to get all data values stop when we have 10 values x x Or when the user enters a zero height for curr_data_value 0 curr_data_value lt 10 amp amp done 0 curr_data_value x Get the data into the array printf Pleas nter the height for person d or 0 if done curr_data_value 1 scanf Slf amp data_values curr_data_value x If the data was non zero we have another height x If not we are done if data_values curr_data_value 0 num_data_values else 106 Computer Programming Using C Revision 1 3 done 1 Calculate the mean height mean_height mean data_values num_data_values Display it x printf AnThe mean height is lf n mean_height return 0 x x Displays welcome messag void welcome_message void printf Mean Height Calculator n printf Enter the height of each person when prompted n printf Enter 0 when you are done You can enter up to 10 values n n x x Calculates the mean of a set of values x double mean double values int num_values double mean int current_value Initialise the mea
78. Smith and Jonathan A Dell Essence of C for Electronic Engineers Essence of Engineering Prentice Hall 1998 4 Tony Zhang Teach Yourself C in 24 Hours Sams 2000 B 2 Reference Material 5 Brian W Kernigan and Dennis M Ritchie The C Programming Language Prentice Hall 1988 6 Grant Macklem Gregory Schmelter Alan Schmidt and Ivan Stashak Graphics library function reference http www cs colorado edu main cs1300 doc bgi Accessed November 2005 7 Microsoft Developer Network Msdn reference library includes C standard library reference http msdn microsoft com library default asp Accessed November 2005 8 Peter Prinz and Tony Crawford C in a Nutshell O Reilly 2005
79. THE UNIVERSITY of York AS Department of Electronics Computer Programming Using C Laboratory Scripts 2007 2008 Peter Mendham with Dr Andy Hunt Dr Julian Miller Andy Pomfret and Dr Steve Smith September 2007 Computer Programming Using C Revision 1 3 Contents Introduction OVCIVIOW4 6 0 a AS BE A A OES Bak ee Oe ee The Structure of the Lab Course 2 ee How These Scripts are Written Structure and Conventions o ooo Before You Begin OVERVIEW cs ae kes Boe bee oe AR RSs RE a Se he a Ane Bad Ae tee 4 Mapping Your N Drive ia ura aed A A a ee en as Creating a Folder For Your Work 2 0 2 ees Copying a Project a a ete tale A IA da ge be ee ea at ate ere te a Te sas Se Opening the Integrated Development Environment IDE 0 000 Opening a Projectin the IDE a pasi p ee SUT AL Ys 0 toni aE NR a a PA a aS OA EA A ae dr Be Sve I Autumn Term Laboratories 1 A Simple C Program in Microsoft Visual Studio LI OVERVIEWS de Ls eae os A eS Oe EPA ASS ieee TZ etn SW Prt sane hee wed ME et cal E a E a A A MM als oe tae smell i anti a ae de 13 Introducing the IDE oe ee at Bos Bona BA a Ve ee dea ae ds 1 4 Looking at Your First C Program 2 ee 1 5 Compiling Executing and Debugging a C Program o ooo ooo o 1 6 Displaying Text on the Screen o o ooo LZ Graphics OPONE es BE A ee ein Bes 1 7 1 A Simple Graphics Program 2 ee LZZ Some Simple Dra
80. TRING x wherever it appears with Hello World n define HELLO MESSAGE Hello World n A numeric example wherever PI appears x x it will be replaced by 3 14159265 x define PI 3 14159265 int main void x Print a message to the screen printf HELLO_MESSAGE 76 Computer Programming Using C Revision 1 3 Display pi printf Pi 1f roughly n PI Wait for a key press getch return 0 g If you build and execute the program you should find that it displays the following text on the screen Hello World Pi 3 141593 roughly Remember that the preprocessor runs through the source code before it gets to the compiler So the code that the compiler sees looks a bit like this int main void printf Hello World n printf Pi 1f roughly n 3 14159265 getch return 0 Notice how the code was changed by the preprocessor Like the include directive a define is also very simple It is structured like this define tag replacement The define directive tells the preprocessor from now on everywhere you see the text tag replace it with the text replacement Syntax The define Directive define tag replacement Starting from where the de fine directive is written the preprocessor replaces an occurrence of the text tag with the text replacement For example the dir
81. The sequencer you have created is limited to playing only one note at once Have a think about how you might lift this restriction How would this change the information that you store in a structure How would the playback function have to be changed Could you incorporate changes in instrument into the sequence Try implementing a few of your ideas 11 7 Summary This lab has introduced you to structures a powerful way of collecting together information An array collects information but a structure is often useful because e the different parts of it members may have different types e the members are named rather than simply referred to by index The middle part of the lab introduced type definitions and showed a way in which they are commonly used when defining structures You should also have used a collection of structures in an array both in a simple example for storing student details and in the graphics and music options The graphics option used an array of structures to deal with graphical objects such as lines in a similar way to vector graphics editing programs The music option used an array of structures as the basis for a simple sequencer 160 Computer Programming Using C Revision 1 3 Laboratory 12 Pointers and Passing Parameters by Reference 12 1 Overview This laboratory begins by investigating how parameters are normally passed to functions When a function is called the value of an argument i
82. _number Generates a random number int random_number int lower_range int upper range The random_number function returns a random number which could be anywhere in the range lower_range to upper_range including the values lower_range and upper_range For exam ple pitch random_number 60 71 will assign a value to pitch that could be 60 71 or any integer value in between random_number is defined in midi_lib h Exercise 5 12 Improvising with Whole Tone Scales Using the function you have just written which plays whole tone scales try to use the random_number function to make your program improvise pieces of music based on whole tone scales Drone tones and dynamics should also be improvised How can you make it sound reason ably musical All the improvisation your program does at the moment is based on whole tone scales Whole tone scales have an interesting effect but their use can become quite constraining You now have the chance to add to your program to make it insert passages of freer improvised melody in between sections of whole tone scales This will all be based on random numbers Here are some things to think about Revision 1 3 Computer Programming Using C 101 e you might like to control the lengths of the free and whole tone scales sections to enforce some kind of structure with recognisable phrasing e you could use a random number to decide whether you are about to improvise a phr
83. _x pos_y initial_pos_y vel_y time gravity time time 2 You should be able to see that the first line works out what the current time must be since the throw using the current z position This line is a simple rearrangement of equation 3 1 Make sure that you understand this rearrangement before continuing The second line is simply equation 3 2 To keep accuracy in all of these calculations we must declare some of the variables as being of double type i e they may contain real valued numbers We will be drawing the path of the object in the graphics window Rather than try and draw a curved line we will construct a curve out of lots of very small straight lines There are two useful graphics functions which we are going to use for drawing the path of the object The first allows us to give the graphics system a current location The function call moveto 100 300 does not draw anything in the graphics window It simply tells the graphics system that we wish to set the location 100 300 to be our current location We can then use the 1ineto function The function call lineto 200 350 draws a line in the graphics window from wherever the current location is to the coordinates specified in this case the coordinates 200 350 It then sets the current location to be 200 350 ready for us to use lineto all over again 66 Computer Programming Using C Revision 1 3 Function Reference
84. a In C you must declare a variable before you can use it To declare it you must give it a name and a type The types you will use the most in Care e int for integer numbers both positive and negative such as 500 2 and 20 e char for single characters such as d and V e double for decimal or real numbers both positive and negative such as 0 05 3 141 and 2 718 Variable names can be as short as a single letter or very long indeed It helps to give variables descriptive names to help you remember what they are for A variable name or identifier can contain any of the following characters e upper and lower case letters a z A Z e the digits 0 9 e the underscore character _ Variable names may not start with a digit Variable names are case sensitive that is upper and lower case letters are treated as being different Some examples of valid variable names are e distance to tokyo ej e anotherCounter Some examples of invalid variable names are e 2me2you it starts with a number e dot dot it contains an invalid character Notice that there is a semi colon at the end of the line Every C program is split into statements in a very similar way that English is split into sentences Every sentence in English ends with a full stop or period Every statement in C ends with a semi colon The next two lines of code are 18 Computer Programming Using C Revision 1 3 distance_to_tokyo
85. a ek a aa lada ra S 63 The 2nelud Directive 2 2 amt o ee i ek Oe AS hee A Re te ee a o ee 75 The tdt ie Direc veri sanea is eek Bw ee A we eas ee a ee Fee ae BR 76 The if and endif Directives ee 80 Function Definitions sste sa Goatees Si 4 Svea od BE a Ol Oe ae ee ld we ee ee we oe 92 Array Declarations ores si a tt Eb Re ER ee ee as e 104 Structures shy a te aa Bod Mak de oS od nta da da dh obit ies AA NM 153 Type Definitions via a AA A AA E Ea a ee 155 Pointer Reference and Dereference Operators o 168 Pointer to Structure Member Access Operator a ooa 170 Thersizeot Operator eva le a AA A a Be a e Oh ea a 179 Introduction Overview This section gives a brief introduction to the structure of the C Programming Laboratory course and the way in which these scripts are written The Structure of the Lab Course There is a C programming laboratory once a week every week from 2 to 10 in both the Autumn and Spring terms There are four laboratories weeks 2 to 5 in the Summer term There is a laboratory script for each lab in the Autumn and Spring terms The content of the summer term labs will be clear when you come to do them You can work through each lab at your own pace however you will be expected to complete one laboratory s script before the beginning of the next lab If you have not finished a script by the end of a lab you may have to complete it in your own time Each lab contains two optional s
86. about it in much greater musical and technical detail For now we will just be using it to get the computer to play sounds Producing MIDI sound output in Windows is quite complicated so this laboratory course uses a set of functions which are explicitly intended for creating sounds easily on Windows This set of functions is an example of a software library 1 8 1 A Simple Music Program If you have a project open at the moment the first thing you must do is close it Select File Close Workspace to do this You should then take a copy of the project musicl and open it in the IDE Check back to the Before You Begin section if you cannot remember how to do this The musicl program behaves quite simply at the moment It plays a single note a middle C for a second and then stops Try building and executing music The source code for musicl c is shown below A program to demonstrate simple musical operations x C Programming laboratory 1 x This line allows the compiler to understand the x midi functions include midi_lib h Revision 1 3 Computer Programming Using C 33 x x The main function the program starts executing here x int main void x Declare integer variables for specifying a note x int pitch channel velocity Set the pitch variable to 60 which is middle C x pitch 60 x We will play the note on MIDI channel 1
87. ah lado Dae Le e Oe es 130 8 9 9 Implementation 2 4 2 208 shoe e ew dA ER ww sone pase a ee AS 134 8 3 4 Extending the Design o ooo o 134 Revision 1 3 Computer Programming Using C iii II 10 11 12 13 14 15 8 4 Music OPON nt Gnd ad SRAM Sita Ae do anata BN teh Ae Be td 135 841 Specifications eva id wane Yee a Sete eres e 135 842 DESTE y Sis A eee al hte Sed Eee ME EE Se age ieee SOE GS 135 6 4 3 Implementation drama a e he bee we oo aries geen a ae 139 844 Extending the Design o ed area BA EE ee EN aa 140 8 5 Writing Your Own Report ee 140 8 521 Requirements i Tor a od Behe id Ee Rice eee de eae 140 8 5 2 ANALYSIS m mi 8 sagen a Sa keene Se de ead Re Rak be BE Beets Pg 141 8 9 3 SpecificatiOnes seuns 2g ae eee Faw a ace ee aul ee ale had dob tele 141 804 Desi tks wh betes a Be a Se atthe iN a a e DETR On ae tab 141 8 5 5 Source Code Implementing the Design 2 ooo ooo o 142 8 5 6 Implementation Report o ee es 142 6 5 7 Verificatiorrand Testing secure Ge a a 142 8 5 8 User Mantal Sa sb he a Gen oo Ga hd ee Ala A ee RG le oe 143 856 Summary ths AES be ata we Oa ale O Bete A 143 Assignment Work 145 9T AOVERVIEW ae aah Be ek ake a Bowie inca ek A eed a pela laa 145 Spring Term Laboratories 147 Assignment Demonstration 149 TOA RN 149 Structures and Defining New Types 151 WT OVERVIEW eyo hos eth he ocd A A a A at ee
88. ar to removing from either the head or the foot The object to be removed will have a structure both before it and after it in the list The steps are e Set the next pointer of the previous structure in the list to reference the next structure in the list e Set the previous pointer of the next structure in the list to reference the previous structure in the list e The structure is no longer part of the list its memory can be deallocated Removing the Only Remaining Structure in the List When there is only one remaining structure in the list the removal operation is simple Both the first pointer and the last pointer should be set to NULL The structure has then be removed from the list and its memory can be deallocated Exercise 16 3 Creating a Double Linked List Change the lab15 program so that it uses a double linked list You may need to draw some dia grams of your own to make sure that you fully understand the processes involved in both adding and removing items from the list You should find that using double linked list simplifies some aspects of list handling 16 5 So When Are Linked Lists Useful Linked lists are a very powerful technique but as you have seen from this and the previous laboratory are more difficult to work with than a simpler storage system such as arrays Linked lists are appropriate in many situations here are some pointers to help you identify when a linked lis
89. are not such as the graphics and music libraries With most modern compilers including the one you are using using quotation marks instead of angle brackets or vice versa will not stop your program from working 4 4 Using the Preprocessor for Text Substitution A lot of Windows programs like Microsoft Word have the facility to search the text of a document to find a particular bit of text that you specify This is called Find You may also have come across the facility also in Word to find bits of text and automatically replace them with another bit of text that you specify This is usually called Replace and is an example of text substitution The C preprocessor has a facility for doing text substitution for you It allows you to define keywords of your own which will get substituted for usually more complicated bits of text which you specify This is done using the define preprocessor directive Copy and open the lab4 project This is a very simple example of how to use the define directive for text substitution The source code for lab4 c is shown below x A program to demonstrate the use of the define directiv x C Programming laboratory 4 x These lines allow the compiler to understand the x printf and getch functions include lt stdio h gt include lt conio h gt An example use of the define directive x The preprocessor will replace HELLO_S
90. art of a define directive It is used in the following way if defined SOME_TAG ndif You can form more complicated tests using the logical operators amp amp and The not operator is perhaps the most useful For example if defined SOME_TAG ndif In this case the guarded code would only be compiled if the tag SOME_TAG is not defined There are two very useful abbreviations for these simple operations ifdef SOME_TAG is short for if defined SOME_TAG ifndef SOME_TAG isshortfor if defined SOME_TAG Exercise 4 6 Investigating Conditional Compilation 2 Change the i directive so that the code is compiled only if DEBUG is not defined You will need to use the information in the syntax box about the if and endif directives to do this if directives are very useful for including code such as printf statements which you only want to use for finding problems in your code debugging It means you can add lots of extra statements to your program and stop them from being seen by the compiler by removing a single define line from the top Even better if you find similar problems again you can add the lines back into your program again by putting just one define line back Using if directives for including special lines for debugging is a very useful technique in situations where stepping through your code is tedious For example ins
91. ascending four times followed by five notes of the same whole tone scale ascending from the same starting note four times followed by six notes of the same whole tone scale in a similar manner as previously four times followed by seven notes of the same whole tone scale four times Finally the last whole tone scale should be played in descending order to complete the piece You will need to put one for loop inside another to get this to work Putting one programming structure inside another is called nesting If you do not understand how to do this ask one of the demonstrators for help 3 6 3 Adding to Your Whole Tone Scale Piece You can hear the patterns in this piece but it probably doesn t sound very musical One reason for this is that there is no properly defined rhythmic structure there is no sense of where the bar lines might be Exercise 3 12 Making the Piece Sound More Musical Without destroying your nested for loop structure alter your code so that each ascending scale takes the same amount of time no matter how many notes are going to be played You will need to calculate the note durations inside the loop What other changes can you make to try and make the piece more musical Can you make the second and fourth scale in each set quieter than the first and the third without changing the for loop structure 70 Computer Programming Using C Revision 1 3 Exercise 3 13 Adding
92. ase based on whole tone scales or completely random notes e you should use random numbers to allow the program to make choices about pitch and note length for example but you might want to place certain constraints on what it can do to make sure the results still sound musical e you will have to be careful with the improvisation between the whole tone scale phrases to ensure that the piece does not become too disjointed Exercise 5 13 Adding to Your Improvisation Program Create a separate function which chooses a note at random and plays it You might like to call it random_note You should use this function to create the free phrases You will need to think about what parameters the function needs so that you can control the random notes it produces You might like to control and have parameters for e the range in which the pitch can lie e the velocity of the note e the length of the note e whether there is a rest before the note Improvising in this way is hard but see how musical you can get it to sound You might find that it is easier to produce a convincing piece if the tempo is kept fairly slow e g adagio 5 9 Summary In this laboratory you should have learned why functions are useful and how to create functions of your own You should understand how to specify parameters and return values and how to declare function prototypes so that you can choose the order in which functions are declared Funct
93. asons for wanting to structure your code into multiple files and how to apply these techniques to other projects You should also have spent some time making sure that you code is well formatted well commented and easy to read You are now ready to tackle larger projects 128 Computer Programming Using C Revision 1 3 Laboratory 8 Practical Software Design 8 1 Overview This laboratory looks at the process of designing software and documenting the development process in the form of a report The lab is split into two parts e the first part of the lab sections 8 3 and 8 4 gives you an existing design for a piece of software This is exactly the kind of design that you will be expected to produce You will implement the design in C and then add to the design to give you practice at designing software e the second part of the lab section 8 5 is a reference guide giving you some simple tips to help you write your own software development reports Section 8 2 will introduce you to the lab and the software development process 8 2 The Structure of Software Projects This laboratory is a bit different to the ones you have done so far In this lab rather than look at another part of the C programming language we will look at how you should use the C that you already know about in a formal software development process The best way to produce good quality software is to follow a well structured software engineering approach
94. at deal Most of the time you have used called existing functions such as printf and getch However every program you have written has contained exactly one function of your own main In this lab you will see how to write other functions which you can call in exactly the same way as printf getch and others Copy the lab5 project and open it in the IDE This project will introduce two new concepts e creating new functions of your own and calling them e using the fflush function to handle bad input from the user when using the scanf function The source code to lab5 c is shown below x A program to demonstrate function creation x C Programming laboratory 5 86 Computer Programming Using C Revision 1 3 include lt stdio h gt display_welcome function displays a welcome messag x The display_welcome function takes no parameters and does not return anything void display_welcome void printf Welcome to the squaring numbers program n n square function squares an integer number The square function takes a single integer parameter It returns an integer which is the square of the value of the parameter it was given SR A E int square int value int squared_value squared_value value value return squared_value x The main function the program starts executing here x The main function takes no parameters and returns an x integer int main voi
95. at you are passing the scanf function a pointer to the my_integer variable which allows it to change the value This is another example of passing by reference Exercise 12 5 Using scanf with a Pointer Alter the change function so that it asks the user what value they wish to set the variable to It should then set the value of the location that i references using a scanf function call Be Careful Remember that the variable your are using 1 is a pointer Do you need to use the reference operator when calling scanf If you don t understand this ask one of the demonstrators to explain it to you before continuing Exercise 12 6 Passing Multiple Values by Reference Because a pointer is just another parameter a function can accept a number of pointers as parame ters as well as other values There are no limitations on this Change the lab12 program so that the change function accepts two or more pointers as param eters and sets the values of them using scanf function calls 12 5 Using Pointers with Structures One of the most powerful ways to use pointers is in combination with structures like those you met in lab 11 By passing a pointer to a function by reference it allows that function to change any of the members of that structure Suppose we have a student _type structure type just like the ones you looked at in lab 11 170 Computer Programming Using C Revision 1 3 typedef struct long_stu
96. ate the memory for the new item e set appropriate member variables in the new item Family Name Given Name Year of Birth Course Code Next Pointer Family Name Given Name Year of Birth Course Code Next Pointer Family Name Given Name Year of Birth Course Code Next Pointer Family Name Given Name Year of Birth Course Code Next Pointer Bloggs Fred 1982 606 0x45678901 Jones Francis 1974 636 NULL Bloggs Fred 1982 606 0x45678901 Jones Francis 1974 636 NULL e set the next pointer of the new item to be whatever the current value of the first pointer is e set the first pointer to reference the new item You may notice that if you try to apply these steps to the first situation where the very first item is being added to the list they will still work In fact these steps will always work for adding new items to the list however full or empty it already is Removing items from the list is the exact reverse of the steps for adding except some are unnecessary e use the first pointer to find the first structure on the list this is the one we will remove e set the first pointer to be whatever the next pointer of the structure references this causes the list to bypass the structure we want to remove e free the memory for the item it has been removed from the list These steps may be translated directly into code The re
97. ated as false On the other hand in this example if 1 endif the code between the if and endif directives will always be compiled because a non zero value is treated as true It is not common to use if directives with a constant value after them like this It is more common to use them like this define ADD_EXTRA_FUNCTIONALITY 0 if ADD_EXTRA_FUNCTIONALITY endif This means that the compilation of the section of code between the if and endif directives is de pendent on the value that the ADD EXTRA_FUNCTIONALITY tag has defined as its replacement In the case above the code between the if and endif directives would not be compiled Rather than test the value of a defined tag it is more common to test whether a tag has been de fined at all You have already seen how to do this in the example program 80 Computer Programming Using C Revision 1 3 Syntax The if and endif Directives if condition endif The if directive tells the preprocessor to remove all the parts of your program until the next endif directive only if the condition is false When testing the condition a value of 0 is in terpreted as false a non zero value is interpreted to be true The most common way to use the if directive is with the special preprocessor syntax defined tag This tests to see if the specified tag has been previously specified as p
98. ave used the scanf function to get input from the user As you have seen the scanf function collects input and allows the program to continue only after the user has pressed enter Sometimes you want to make a program that is more interactive than this In this section we will use the get ch function to collect a single key press from the user The get ch function waits for the user to press a single key and then returns the value of the key that the user pressed back to the program as a character The get ch function is described in conio h so to use it you must add the line include lt conio h gt to the top of your source file You would use get ch in the following way int key_entered Revision 1 3 Computer Programming Using C 51 key_entered getch getch will wait for a key press and then the assignment will copy the value of the key as a character into the key_entered variable So if you use the bit of code above you have the value of the key press in a variable Now you need to know how use the value You can describe the value of a character in C by enclosing the single character in single quotation marks Like this if key_entered r printf You pressed the R key n Function Reference getch Obtains a single key press from the user character getch The get ch function waits for a key press on the keyboard and then returns the value of the key that was pressed as an integer
99. ays be structured like this if number_entered lt 10 printf That s less than 10 n Notice how the printf line is indented by one tab character relative to the if clause The next line after this one is not part of the if statement and so should start in the same vertical position as the if clause The editor in the IDE will try to carry out the correct indentation for you automatically Sometimes however it may get it wrong You can move a line to the right by placing the text cursor at the beginning of the line and pressing Tab which inserts a tab character You can move the line left by holding down the Shift key and pressing Tab In the IDE editor this also works with blocks of code If you highlight a block of code like this The integer placeholder was not matched if num_placeholders matched lt 1 Clear out whatever the user typed fflush stdin loop will go again Please try again Tell the user to try again rintf That was not an integer while num_placeholders_matched lt 1 and press the Tab key the editor inserts a tab character at the beginning of every line in the block The block of code therefore moves to the right The integer placeholder was not matched if num_placeholders matched lt 1 Clear out whatever the user typed ZA loop will go again Please try again Tell the user
100. ber that is returned and plays a note as necessary The main function uses three variables Variable Range C Type Description leave Oorl int 0 indicates that the program should continue run ning 1 indicates the program should finish key a A w W Ss S e int The number of the key that was pressed by the user EROS DES BR ity ods E GOG y Y K Hu U 5 TJ Kk K q Q pitch 60 72 0 1 int The pitch of the note to play or zero if the note should not be played or 1 if the program should exit The detailed algorithm for the main can be described in pseudo code as follows function main 138 Computer Programming Using C Revision 1 3 call display_welcome function call display_keys function set leave to be 0 begin loop call getch to get a key from the user put the result in key if key is zero then call getch again putting the result in key end if call key_to_pitch passing key assigning the result to pitch if pitch is equal to PITCH_QUIT set leave to be 1 else if pitch is not equal to PITCH_INVALID turn on a midi note of pitch on channel 1 with velocity 64 pause for NOTE_DURATION turn off a midi note of pitch on channel 1 end if loop while leave is equal to 0 end function main The two display functions are very simple The display welcome function simply displays the first part of the welcome message T
101. between arrays and pointers An array is essentially a pointer to a block of memory locations which the C compiler has set aside Array and pointer notation can therefore be used interchangeably A pointer on its own is not very useful as it has no memory to refer to This lab introduces the malloc function which you can use to allocate blocks of memory whilst your program is running Any memory you allocate with malloc must be de allocated before your program ends using the free function C provides an operator called sizeof which helps you determine how much memory is required by different variable types Finally the lab looks at allocating memory for structures and arrays of structures You will alter the graphics or music program you have been working on to use the memory allocation functions malloc and free 13 2 More About Arrays Lab 6 introduced you to arrays You may remember diagrams of arrays with boxes representing the elements of the array Like this o my_array hb No my array w my array The boxes in array diagrams like this one represent memory locations in just the same as the boxes in the diagrams representing pointer variable relationships in lab 12 These diagrams simply the way in which arrays work An array actually has two parts to it e A block of memory locations in which the information for each element is stored e The array variable is actually a pointer which references the first memo
102. ble to use it In software engineering this is called encapsulation e they allow you to use parts of your program many times without having to re type the same bits of code Logically enough this is called code reuse If you choose the names of you functions wisely then what they do should be fairly clear just from looking at a function call This will make your programs easier for you to write and debug Carefully crafted functions have the potential to be used more than once in a program which saves you effort Or you could copy and paste a function out of one program and into another if you think it will be useful As an example the get_ double function you have just written is very useful It gets a double value from a user and does some input validation There are likely to be many times in the following labs and in the assignments when you need to get a value in this way You might find it useful to reuse the function by copying it and pasting it into a different program You can only do this so easily because it is a separate function 94 Computer Programming Using C Revision 1 3 5 5 Positioning Functions in a File In the example program you have just modified the functions display_welcome square and get double were defined before the main function Exercise 5 5 Changing the Order of Functions in a File Move the get_double function so that it is defined underneath main You could use Edit Cut and Ed
103. calls a graphics function to display the graphics window initwindow 640 480 Calling the initwindow function in this way produces a window 640 pixels wide the x direction and 480 pixels high the y direction 28 Computer Programming Using C Revision 1 3 Function Reference initwindow Creates a graphics window of a specified size initwindow width height e g initwindow 640 480 The initwindow function creates the graphics window to allow you to begin drawing in it The graphics window will be created with a drawing area of the specified dimensions i e it will be width pixels wide and height pixels high When you have finished with the graphics window you should close it with the closegraph func tion initwindow is defined in graphics _lib h The next two lines set the coordinate variables to the point at which we are going to draw the circle X_position 100 y_position 340 This position will be the centre of the circle Before we do any drawing we set the colour that we will be using to draw with setcolor RED Calling the setcolor function does not produce any output on the screen It changes the colour that will be used for future graphics functions It is the equivalent of picking up a pen of a specific colour Revision 1 3 Computer Programming Using C 29 Function Reference setcolor Sets the current drawing colour setcolor colour_number The set color function
104. code The need to include prototypes for each function called in another file is inconvenient when you want to use one source file in more than one project The easiest way to solve these problems is to place the prototypes for all the functions in particu lar source file into a header file with the same name For example assume that a source file called graph fun c contains the following functions Revision 1 3 Computer Programming Using C 123 e show_hello e draw_stick_person e draw_throw To accompany this source file a header file called graph fun h should be created A header file is just like a source file except that the code that it contains shouldn t be code that actually executes For example the header file graph_fun h will only contain function prototypes The function prototypes will used by the compiler and linker to match up the functions in graph fun c to other files in which they are called The function prototypes themselves are not converted into executable code In our example the header file graph_fun h should contain the prototypes for the three functions in graph_fun c For example the contents of graph fun h might be as follows x Header file for graph_fun c Function prototypes only x void show_hello void void draw_stick_person int x int y void draw_throw int x int y double velocity As you can see header files can be very short In the f
105. ct correspondence between instrument numbers and instrument sounds or voices is dependent on the sound card being used Revision 1 3 Computer Programming Using C 37 Function Reference program_change Changes the current instrument on a MIDI channel program_change channel voice e g program_change l 51 The program_change function changes the active instrument on the channel specified by channel channel should be an integer number from 1 to 16 the same as used in the midi_note function The instrument is selected using the voice argument This should be an integer number between 1 and 128 Each number corresponds to a different instrument The instrument that a given number corresponds to is defined by the General MIDI specification which most MIDI devices adhere to Some common instruments and their voice numbers are 1 Acoustic Grand Piano 43 Cello 7 Harpsichord 49 String Ensemble 10 Glockenspiel 51 Synth Strings 13 Marimba 57 Trumpet 17 Drawbar Organ 58 Trombone 27 Electric Jazz Guitar 66 Alto Sax 28 Electric Clean Guitar 67 Tenor Sax 33 Acoustic Bass 74 Flute 41 Violin 119 Synth Drum Check MIDI documentation for example on the internet for more information program_change is defined in midi_lib h Exercise 1 10 Changing the Program Experiment with using program_change to change the voice that is being used to play your tune Exercise 1 11 Creating both Melody and Chords Use the p
106. ct you should see that it is nearly identical to lab3 except that it uses a for loop instead of a while loop It also declares an extra variable count to use as a counter in the for loop Try compiling and stepping through lab3a A program to demonstrate the use of the for statement x C Programming laboratory 3 x include lt stdio h gt int main void x Declare a variable to store an integer number x int number_entered Declare a counter variable x int count Output some text to the user x printf Enter an integer number Wait for the user to enter a number and hit enter x x Store the number in the number_entered variable scanf d number_entered x Display all the numbers from the one entered x up to and including the number 10 x for count number_ entered count lt 10 count printf din count return 0 At the beginning of a for loop after the keyword for is a set of parentheses with three statements inside You can understand how these statements work by noticing that any for loop can be written as a while loop In general the for loop for statementl statement2 statement3 statement_to_loop can be written as an equivalent while loop like this statementl while statement2 statement_to_loop statement3 Revision 1 3 Computer Programming Using C 61 To help this make sense lets look at the example in
107. ction is called strcmp The strcmp function takes two arguments both of which are strings For example 222 Computer Programming Using C Revision 1 3 char first_string hello char second_string world int result result strcmp first_string second_string The strcmp function compares the two arguments and determines the order they should be in alpha betically and returns an integer number If the first argument comes before the second strcmp will return a negative number If the second argument should come before the first st rcmp will return a positive number greater than one If the two arguments are identical st rcmp will return zero The st rcmpi function is identical to the st rcmp function except that st rempi ignores the case upper or lower of the characters when it carries out the comparison Function Reference strcmp strcmpi String Comparison sia Sica Cleese Scriting Clasicas Siewaliae 2 y aj SiccaoL Cheis STen Clases sSiewaliae 2 p e g estudie Serie e reS tes Erino Secomel_ Sieiesiove f security_check strcmp Open Sesame password are_not_equal strcmpi magic abracadabra The strcmp and strcmpi functions compare their two string arguments string1 and string2 In each case the function returns an integer indicating the relative order of the two strings e if stringl comes before string2 the function returns a number less than zero e if stringl comes after s
108. ctions If you do not understand how to step into the display welcome and square functions ask one of the demonstrators You should find that any variables defined in the body of the main function are not available in other functions When the point of execution is in the square function there is one variable available squared_value Variables defined inside the body of a function are known as local variables because they are local to the body of the function The section of the program in which a variable is valid i e the function body that contains it is known as the variable s scope Exercise 5 2 scanf Input Validation The code which surrounds the scanf function the code inside the while loop validates the user input to make sure itis of the correct type Try running the lab5 program and typing in text instead of a number What happens Try stepping through the program in the debugger and give the program the same input Make sure you understand how the program works before continuing If you need any help ask one of the demonstrators 5 3 Anatomy of a Function We are now going to look at how a function head is constructed so that you can define functions of your own There were two functions defined in lab5 display welcome and square The function head for display_welcome looked like this void display_welcome void voidis a type like int and double except that its main use is in fu
109. cture 012345678 students 0 0x12345678 Family Name 7 Given Name Undefined students 1 Year of Birth Course Code Undefined students 2 Undefined students 3 The variable that keeps track of how many students there are in the array must also be incremented As each element of the array is now a pointer to a structure we must use the gt operator to access the structure members Like this students 0 gt year_of_birth 1986 Removing a student from the end of the list is just like removing an item from a LIFO buffer The only difference is that we must use the free function to deallocate the memory that was being used by the structure we have just removed Revision 1 3 Computer Programming Using C 195 Exercise 15 1 Using Arrays of Pointers If you have been following the graphics option open the graphics3 project if you have been following the music option open the music3 project In lab 13 you changed the program so that the array of structures was allocated dynamically and deallocated at the end of the program Replace the dynamically allocated array of structures with a statically allocated array of pointers to structures This will make it easier for you to allow the user to add and remove lines notes You will need to keep track of how many of the elements of the array are in use You might like to use the LIFO buffer code from lab 14 as inspiration for this Use dy
110. d int num_placeholders_matched int number_entered squared_number x Call the display_welcome function x This will display a welcome message display_welcome Obtain a number from the user x printf Please enter an integer number x Loop for as long as the user gives us values that aren t integers do x Call scanf and use the return value to find out x how many placeholders were matched num_placeholders_matched scanf d amp number_entered x The integer placeholder was not matched x if num_placeholders_matched lt 1 Revision 1 3 Computer Programming Using C 87 Clear out whatever the user typed fflush stdin x Tell the user to try again loop will go again x printf That was not an integer Please try again while num_placeholders_matched lt 1 x Square the number using the square function x squared_number square number_entered Display the result x printf d squared is d n number_entered squared_number return 0 All the programs you have seen so far have started with the main function This program is no different it s just that there are two other functions included in the source code before the main function These two functions are called display_welcome and square The first thing that the main function does is to call the display welcome function which it does with this line
111. d amp before the variable name Revision 1 3 Computer Programming Using C 41 Function Reference scanf Obtains a line of input from the user variable scanf format_string amp data_item e g sieeuoie Vc Main aint yveutilelo e seerne Wo Se Chian yeisilelo le number_of matches scanf S1f a_double variable The scanf function obtains typed input from the user It lets the user type in text and then waits for them to press Enter It then takes the text that they have entered and attempts to match it to the place holders specified as part of the format_string It takes the following arguments e format_string contains the place holders that scanf will try to match input to enclosed in double quotes e data_item these are variables which will be set to the values recovered from the user s input scanf uses the same place holder system as printf As a reminder the most useful place holders are e d for integer int variables e Sc for single characters char e 1f real valued double variables The place holders are matched with the comma separated data item variables in order The return value of scanf the value that is assigned to variable is the number of place holders that were successfully matched scanf is defined in stdio h Exercise 2 1 Changing the Variable Type Alter the lab2 program so that it accepts real valued numbers from the user no
112. d int_variable fprintf result_file The answer is Sd integer_answer num_chars fprintf temp_file Slf double variable The fprintf function works like the printf function except that instead of outputting its results onto the screen it places them into the file specified by the ile_handle argument It is called in exactly the same way as print f but with an extra first argument file handle fprintf takes at least two arguments but like printf it can take more depending on how many variables you want to include e file handle isa handle to a file previously opened with fopen which will be used as the destination for all fprintf write operations e format_string is a string containing placeholders just like with printf e after the first two arguments where the is you should include variables whose values will be substituted for the placeholders in the format_string The placeholders you will use most often are e Sd for integer int variables e 1 double variables e Sc for single characters char e s for strings char These are the same as for printf The return value of fprintf is an integer which specifies how many characters were written into the file not including the null termination This number will be negative if an error occurs The fprintf function is defined in stdio h Exercise 17 1 Investigating File Writing Try building and executing the lab17 pr
113. d scanf function call There is no reason why this has to be the case A fprintf function call could insert multiple numbers into a file like this fprintf file_handle d d n first_number second_number This would write two numbers on a single line in the file separated by a comma and a space To read these numbers back in from the file we would use the following scanf function call fscanf file_ handle d d n amp first_number amp second_number There is also no reason that we must only work with numbers We may also work with strings In labs 11 15 and 16 you worked with a structure which stored information about a student You created a type definition for this structure called student_type To write information from this type of structure to disk you would use a piece of code like the following fprintf file_handle s student family_name fprintf file_handle s student given_name fprintf file_handle d student year_of_birth fprintf file_handle d n student course_code Notice that each of the pieces of information about the student will all appear on the same line in the file each separated by a space and a comma A similar system could be used for reading information in 220 Computer Programming Using C Revision 1 3 Exercise 17 6 Reading and Writing Structure Information to from a File Alter the lab17 program so that it prompts the user for details about a
114. d check that you understand what has changed and why Do you understand what the program is doing e How do the calculations compare with the results you obtained with a calculator e If the results are different why are they different If you can t answer these questions ask one of the demonstrators for help Revision 1 3 Computer Programming Using C 23 1 6 Displaying Text on the Screen We are now going to add a statement to the program which calls a function to put some text on the screen The function we are going to use is called printf To be able to use the function the compiler needs to have some information about the function which is contained in a separate file called a header file You can tell the compiler to look in the header file that is needed for print by putting the following line at the top of your program before the main function include lt stdio h gt This means include information from the header file called stdio h It will allow the compiler to understand the printf function we are about to use After the line time_to_tokyo time_to_fly time_to_drive Type in a new line printf It takes d hours to get to Tokyo n time_to_tokyo Make sure you get the direction of the backslash 1 correct and that you don t miss the semicolon off the end of the line Be careful that you don t change the case of the letters that you type from the ones printed here C always treats lowercase
115. d on a template a layout for the card which we are going to fill in Now that we have a template we can use it We declare a variable called student which is a structure of the template student type Declaration keyword a ie Structure type name struct student_type student Variable name To use the student variable you must specify which one of the member variable you wish to access For example to set the year of birth to 1986 you would write student year_of_birth 1986 Revision 1 3 Computer Programming Using C 153 The dot says that the variable before it is a structure and the variable afterwards specifies which part of the structure we want to access Syntax Structures Sia UC ema amie member variable declarations A structure is a way of grouping variables together where the variables may have different types Structures also create more readable code because unlike arrays each item of data in the structure has a name rather than just a number A structure definition specifies a new structure type called name which has member variables spec ified by the member variable declarations For example the following code defines a new structure type called Point with two member variables x and y suiuci IPosLine aaa Sep mie Yp y This structure definition can also be written Siciuc e POaliae inek We y The member variable declarations follow exactly the same syntax as ordinary variable dec
116. d this limitation 164 Computer Programming Using C Revision 1 3 12 3 Introducing Pointers When you store a number it in a variable the program represents that number as binary and places in the computer s memory In some diagrams in this lab script this process has been shown by depicting the memory location as a box containing the number Like this This diagram appeared in lab 6 You can think of the computer s memory being entirely made up of boxes like this one Some of these boxes are used for your program s variables others are used for your program s code and more are used by other programs Ill int my_integer 20 Every box or location in the computer s memory is numbered The number for a location identifies it uniquely and is called an address You can refer to any location in the computer s memory by specifying its address Since addresses are just numbers it can be difficult to keep track of them so program ming languages give us a way of representing location addresses with names A variable name like my integer is just an easier way of talking about a location in the computer s memory 0x12345678 my_ integer Address Value Name The address in this diagram is made up It is difficult to know what address your variables will have before your program loads Because C gives a name to each variable you don t need to know the address C provides a way to use one variable to refer to the contents o
117. dd a student lt r Remove a student Cq gt Quit Please choose an option Exercise 15 2 Investigating Linked Lists Familiarise yourself with the lab15 program try adding students and browsing through the list You should find that two important functions do not work e the ability to remove a student e the ability to view the previous student in the list e the ability to view the last student in the list When you add a student does the student appear at the beginning or the end of the list The lab15 program uses a structure to store student information in It is defined like this from types h typedef struct long_student_type char family_name 40 char given_name 40 int year_of_birth Revision 1 3 Computer Programming Using C 201 int course_code struct long_student_type next student_type This definition is identical to the structure you used in lab 11 with the addition of a pointer called next Notice that this has to be defined using the long type name struct long student_type rather than the abbreviated student type This is because the structure needs to define the type of the next pointer before the typedef is complete At the point at which the next pointer is defined the student_type type name is not yet valid The program uses another structure to store information about the list as a whole This structure is also defined in types h It is defined like this
118. de Family Name Jones 0x45678901 Given Name Francis Year of Birth 1974 Course Code 636 196 Computer Programming Using C Revision 1 3 In this situation we have a single list the array which tells us where to find each of the structures We could simplify the diagram and show it like this Rather than have an array which has limited size we could simply keep one pointer which only ever references the first structure Like this Structure Pointer Structure Structure We could arrange for the first structure to contain a pointer which references the second structure Structure Structure This process could then continue so that each structure contains a pointer which references the next structure in the list Revision 1 3 Computer Programming Using C 197 site F since y Pointer gt Site Suc It is then possible to find any item in the list simply by starting at the beginning and following each of the references in turn The list can now grow to any size An empty list consumes as much space as one pointer This efficient way of storing information is known as a linked list because the list of structures is linked together by references A linked list is usually created by adding an extra member variable to the structure The member vari able is a pointer which references the next structure in the list 0x12345678 Family Name Smith 0x12345678 students
119. de specified by the access_mode argument Both of these arguments should be strings Valid access modes are e r open file for reading the file must already exist e w open file for writing if the file already exists it will be overwritten e a open file for writing if the file already exists it will be not overwritten writing takes place at the end of the file this is called append mode e r open file for both reading and writing the file must already exist e w open file for both reading and writing if the file already exists it will be overwritten e a open file for both reading and writing if the file already exists it will be not overwritten reading and writing take place at the end of the file If the file cannot be opened the fopen function returns NULL The fopen function is defined in stdio h Function Reference close Closes an Open File ime relose Pls ii le aemelle y The fclose function closes an open file identified by the argument file_handle If there is a problem during the close operation the fclose function returns the predefined constant EOF If there were no problems the function returns zero The fclose function is defined in stdio h 17 3 Simple File Read and Write Operations Copy the lab17 project and open it in the IDE The source code for the lab17 c file is shown below x A Program to Demonstrate File Handling x Lab 17
120. dent_type char family_name 40 char given_name 40 int year_of_birth int course_code student_type We could declare a function to accept one parameter which was a pointer to a structure of this type void change_student student_type student So that parameter student is a pointer to a structure of type student_type So how would the change_student function set the values in the structure It can t do it like this student year_of_birth 1986 because student is a pointer to structure not a structure We need to use the dereference operator to follow the reference to find the actual st udent_t ype structure It has to be done like this student year_of_ birth 1986 This dereferences the pointer student to find the structure then uses the dot operator to access the member variable year_of birth The brackets are necessary because otherwise the takes prece dence over the x and C thinks that the star refers to both the parts before and after the Writing student member is very cumbersome and difficult to read To alleviate this problem C includes a special operator for accessing the members of a structure to which you have a pointer It looks like this gt It is a combination of a minus sign and a greater than sign gt and is meant to look like an arrow The line student gt year_of_birth 1986 is exactly equivalent to student year_of_ birth 1986 The firs
121. e Use the mean function to calculate the two means You might want to look back at the last laboratory to remind yourself about the pow and sqrt functions e You will need to include math h 6 4 Initialising Arrays and Multi Dimensional Arrays Sometimes you will want to make sure there are specific values in elements of an array before you do anything with it Imagine a situation where you want to know the number of days in a month If you have the number of the month from 0 to 11 in a variable called month you could use an array to find out the number of days the month has int days_in_month 12 printf The number of days in Januray d days_in_month 0 For this to work you would need to make sure the array days_in_month was set up with the right values We could do that like this int days_in_month 12 Revision 1 3 Computer Programming Using C 109 days_in_month 0 31 days_in_month 1 28 days_in_month 2 31 days_in_month 3 30 days_in_month 4 31 days_in_month 5 30 days_in_month 6 31 days_in_month 7 31 days_in_month 8 30 days_in_month 9 31 days_in_month 10 30 days_in_month 11 31 But this is a pain Fortunately C provides us with a way to initialise the value of an array when we declare it Like this int days_in_month 12 31 28 31 30 31 30 31 31 30 31 30 31 The values on the right hand side of the assignment operator in t
122. e demonstrators 5 4 Functions Why Bother Why did you move the input handling code into a separate function in exercise 5 4 One answer is that it made a very important part of your program the main function more readable Readability is something that you as a programmer should be very worried about As a general rule programs are read about 10 times more often than they are written When you come to write bigger programs you will need to be able to glance back over code that you have written previously and still understand how it works If a program is being designed and written by more than one person as is usually the case in industry the problem becomes even greater One software engineer s code may be read by many others who need to understand what it does easily and quickly Software may also be used or updated by people other than those who wrote it This is especially common in industry and can be a real problem So making code more readable is one good reason for functions However perhaps the most important reason for functions is that once you ve turned a piece of code into a function you can use it as a building block Just as you have been doing with printf for example Functions do two things which make them powerful building blocks e they hide all the complicated workings of the program and present a simple interface in the form of a function call You do not have to know how a function works in order to be a
123. e last two sections you found that an array is a pointer to a block of memory locations The block of memory is allocated by the C compiler when your program is running The C compiler then sets up the array pointer so that you can use it There are a number of circumstances under which you might not want the C compiler to allocate the memory for you You might want to do it yourself The most common of these reasons are e You don t know how big an array you need until the program is running When you specify an array size it must be fixed when you write the program If you allocate the memory yourself you can control how big an array is whilst the program is running perhaps in response to user input e The amount of memory that can be set aside by the compiler for an array is limited Sometimes you may wish to allocate a large block of memory to use as an array for example to manipulate a bitmap image or a sound sample Allocating memory whilst the program is running is more flexible and the blocks of memory which can be allocated are bigger When the compiler allocates array memory for you you must have specified the size when you wrote the program This size is fixed so this is called static memory allocation Allocating memory whilst the program is running is more flexible This is called dynamic memory allocation because the amount of memory that is allocated can be changed every time the program is run The standard C library provides a
124. e replaced by a compound statement just as with if to give while relational_expression i Revision 1 3 Computer Programming Using C 59 Exercise 3 1 Using a while Loop Alter the lab3 program to display a sequence of numbers which starts with the number that the user entered but which doubles with every number it displays It should stop when it reaches or exceeds the square of the number the user entered Hint you may need to introduce another integer variable Sometimes you know that you want to execute the statements inside a loop at least once We can do this with a while loop by using a do clause The do clause goes at the beginning of the loop and tells C that we are starting a loop but that we don t want it to check the condition until the end It works like this do while relational_expression A couple of really important things to note e the loop will execute while the relat ional_expression is true not until it is true this is a very easy mistake to make e there is a semicolon at the end of the while clause ina do while loop You will probably find that do while loops are more useful than plain ordinary while loops be cause you usually want a part of your program to execute at least once Syntax The do while Structure do statement while relational_expression The do while loop is very similar to a while loop see above except that
125. e to specify a location that results in any part of the stick person being cut off by the left hand edge of the window The user should also not be able to specify a location that is in the right hand half of the window If the user does specify an invalid location you should display an error message and not show the graphics window with the stick person in it The process of ensuring that input is suitable for your program is known as input validation For this exercise to work you will have to make sure that your stick person is not too big You might like to draw in a line representing ground level below the stick person s feet You should now have a working program that allows the user to control the horizontal position of the stick person within bounds which you have specified Revision 1 3 Computer Programming Using C 53 Exercise 2 9 Adding User Control of Colour of the Stick Person The next step is to allow the user to choose the colour of the stick person You should do this by showing the user a menu a list of possible colours and allow them to choose the colour by pressing a single letter usually the one that corresponds to the first letter of the colour e g R for red This should choice should be case insensitive i e r and R should be treated the same You will probably want to use a switch statement for this You should use the default clause to watch for invalid input from the user If the us
126. ecified amount of time o ooo eo 35 program_change Changes the current instrument ona MIDI chammel 37 scanf Obtains a line of input from the user o oo ooo 41 getch Obtains a single key press from the user o o o o ooo oo oo o 51 setfillstyle Sets the graphical style used for fill operations 53 floodfi11 Fills an area with a coloured pattern o ooo ooo o 54 moveto Sets the current graphics location o ooo ooo o e 66 lineto Draws a line from the current location to the specified location 66 kbhit Checks to see if a key has been pressed n 2 1 2 ooo 70 f t sh Flushes a stream s sui a go eh a ae an aoe aca Gude 4 89 sqrt Calculates the square root ofanumber 1 20 2 oe ee 95 pow Raises one number to the power of another number o ooo ooo 96 sin cos tan Trigonometric functions ooo ee 96 asin acos atan Inverse Trigonometric functions ooo o o 96 cleardevice Clears the contents of the graphics window 2 2 ee ee 98 setbkcolor Sets the background colour 1 2 ooo ooo ee 99 outtextxy Draws text in the graphics window 2 a 99 random_number Generates a random number oaoa a a 100 s Using the s placeholder with scanf and printf saasaa aaa a 112 sprintf Forming strings
127. ections e music option intended for Music Technology students e graphics option intended for all other students You must choose one of these options If you have time you may find it fun to attempt parts of the other option The C programming course is assessed through two assignments one in the middle of the course and one at the end For each assignment there will also be two options music and graphics If you have managed to learn techniques from the other option it will make your assignments all the more impressive How These Scripts are Written Structure and Conventions These scripts are intended to be worked through in order however some sections are highlighted to make it easier for you to refer back to important information later in the course The normal text of the script will contain both information and instructions for the tasks you should carry out You must make sure you read the scripts carefully especially before asking for help you may have missed something important Sections where you need to think carefully about what you are doing are shown as exercises and appear like this Exercise 0 1 An Example Exercise Exercises appear in boxes like this one Sometimes you need to do something but the instructions are not given in an exercise box Usually this 2 Computer Programming Using C Revision 1 3 is because the action you need to carry out is fairly simple To make sure these parts of
128. ective CIO NS 2 71828 replaces any occurrence of the text E CONST with the text 2 71828 It is generally considered good programming practice to use UPPERCASE names for define tags to visually distinguish them from variable and function names define directives are used to define replacement tags for two main reasons e To make your program more readable For example Revision 1 3 Computer Programming Using C 77 circle_area PI radius radius is a lot easier and quicker to read and understand than circle_area 3 141592653 x radius radius e To make your program easier to change For example it is common to use a define directive for your program s version number This allows you to put a define directive clearly at the beginning of the source code like this define PROGRAM_VERSION 2 3 Somewhere in your source code perhaps when the program starts you might write printf Welcome to myprog Version 1lf n PROGRAM_VERSION When you make a change to your program you don t have to go looking for all the places where you display the version number you simply change the number in the define directive at the top of the source file Exercise 4 1 Using the define Directive Add to the lab4 example program to e prompt the user for a number the radius of a circle e store the number in variable of type double e calculate the area of a circle with the rad
129. ed Re ad Ae teed 151 11 2 Introducing Structures 2 ee 151 11 3 Defining New Types with typedef 2 ooo oo 154 IVA Using Arrays Of Structures va ii s ages ect ag ae e So Aertel ee E 156 115 Graphics Option iiss st ae ea eaten Grae Act N Sa ey ee he ene js 156 116 Music Option 2k a Se ee ee ee A ae a 158 RS A es Se aha ie ee A A ae ed cay he Bee PS Se BN adh E Da 159 Pointers and Passing Parameters by Reference 161 12 1 OVERVIEW e ee eS de elo te ele 2 A a oe Ae A S eee A 161 12 2 More About Function Parameter Passing o ooo e 161 12 3 Introducing Pointers isis o e E a dae a 164 12 4 Using Pointers to Pass Parameters by Reference o o ooo oo oo 168 12 5 Using Pointers with Structures o oo o 169 12 6 SUMMA a ado o SSA ad ed 171 Arrays and Strings Revisited and Allocating Memory 173 LIL OVERVIEW is a a 4 A e a a la Rs al dele lla 173 13 2 More About Arrays tooo on a Git tat a ae ta ay laa 173 13 3 More About Strings seni aa kd urea a Bk Kk Wie Bok eal ee Pea ner eS 175 13 4 Allocating Memory 176 13 5 Dynamic Memory Allocation for Structures ooo o e e 180 13 07 SUMMAT uo tods e o Re A dy ee et Oe ak A 180 Creating Buffers 183 TAV OVERVIEW a A A e Gea A ee E See i ae ee ln A OB a 183 14 2 Buffers Flexible Storage si ce cego atha a na ee 183 1433 Stacks LIFO Buffers is aa oa eek BO A ee aS RGN S ak GA 184 14 4 Buffer Problems Overflow and Underflow
130. ed in math h Revision 1 3 Computer Programming Using C 97 Exercise 5 7 Calculating the Length of a Triangle s Hypotenuse Alter the lab5 program to prompt the user for two values You should call your get double function twice to do this Treat these two numbers as the lengths of two sides the opposite and adjacent sides of a right angled triangle Use the square and sqrt functions to calculate the length of the hypotenuse using the Pythagorean Theorem Remember to include the math h header file 5 7 Graphics Option 5 7 1 Creating More Manageable Code Open the graphics1 project you have been working on in previous laboratories Your graphics pro gram should operate in the following way e The user is asked for an initial velocity which they type in e The stick person appears on the screen and the user gets the opportunity to move the stick person left and right using the arrow keys e When the user presses Enter the stick person throws an object which is drawn on the screen e The user then has another two goes at this Your program is now getting quite large To make it more convenient you should now split in into multiple functions Exercise 5 8 Splitting Your Program into Functions Define suitable functions for e drawing the stick person at any location on the screen This function should have two param eters which specify the x and y coordinate at which the stick per
131. ed mathematically As an example let s look at a simple C major scale If the scale starts on middle C the first note of the scale has a pitch value of 60 To get the other notes in the scale we could add small pitch values onto this starting value like this Revision 1 3 Computer Programming Using C 117 Pitch 60 0 2 4 5 7 9 11 12 If we chose a major scale in a different key then the pitch offsets would still be the same But the pitch offsets are not related in any obvious mathematical way A way to approach this problem is to store these pitch offsets in an array For example you could define a major scale like this int major_scale 8 0 2 4 5 7 9 11 12 A loop like the following one would play a major scale int scale_note int key key 60 for scale_note 0 scale_note lt 8 scale_note midi_note key major_scale scale_note 1 64 pause 500 midi_note key major_scale scale_note 1 0 Arrays like these are very powerful for representing musical relationships such as scales and chords Exercise 6 10 Making Your Improvisation Use Non Whole Tone Scales Begin by opening your music2 project Add a function which uses as array to play a single as cending octave of a major scale Try using it in place of the function which produced whole tone scales Now is your opportunity to innovate Try and improve your improvisation program focussing on using scales other than whole to
132. eger The amp operator goes this way j The operator goes this way 0x89012345 0x12345678 ref_my_integer To make this clearer let s look at an example piece of code int main void int my_integer int xref_my_integer ref_my_integer amp my_integer my integer 20 printf my integer is d n my integer xrefmy_integer 5 printf my_integer is now d n my_integer return 0 This piece of code is in the project lab12a Copy it and open it in the IDE Exercise 12 2 Investigating Pointers Build and execute the program lab12a Look at the source code and have a go at trying to under stand how the program works Don t worry if you don t understand the next part of the lab will explain this program We will now investigate this program a line at a time The first two lines of the program declare the integer variable my_integer and the pointer variable ref_my_integer which is specified as referencing integers The program has not assigned values to these variables yet 166 Computer Programming Using C Revision 1 3 int main void 0x12345678 my integer int my integer int xref my integer 0x89012345 ref_my_integer IL ref_my_integer my integer my_integer 20 printf my_integer is d n my_integer ref_my_integer 5 printf my_integer is now d n my_integer return 0 The next line uses the amp operator to set up a pointer
133. enclosed in quotation marks then the preprocessor looks for the file in the current folder where your source file is stored before looking in any places that you have specified e If the filename is enclosed in angle brackets then the compiler assumes it is a standard library header file Standard library header files describe functions that are part of the the C standard library functions that are specified as part of the C language This includes functions like printf and scanf in stdio h and getch in conio h It does not include any of the graphics or music functions Revision 1 3 Computer Programming Using C 75 So the preprocessor handles a include by finding the file looking where the angle brackets or quota tion marks tell it to look and substituting the entire contents of the file for the include line Syntax The include Directive include lt filename gt or include filename The include preprocessor directive is completed as part of the preprocessor before the compiler is run The directive identifies a file filename which is usually a header file but can be anything The directive takes the text from the header file and inserts it in place of the include directive The angle brackets and quotation marks determine where the preprocessor looks for the file As a general rule angle brackets are for header files that are part of the C standard library such as stdio h and quotation marks are for header files that
134. ent location will be the end of the new line The amount that a line is drawn by should be small but not too small 10 pixels is reasonable in a 640 by 480 pixel window To allow this amount to be changed easily it should be defined as a symbol Symbol Name Value MOVE_DISTANCE 10 Program Structure Design The program can be split up into separate functions corresponding to the different tasks the program must perform Separate functions are used for programming clarity and to enable code reuse The structure of the program is shown in the diagram below 132 Computer Programming Using C Revision 1 3 display_welcome Start End Each of the structural units in the diagram is a function These functions are documented in the table below Function Name Input Parameters Return Value Description y coordinate Integer main None Integer error level Driving function calls all passed to environ others always returns 0 ment Handles the actual draw ing display_welcome None None Displays the welcome message and instructions to the user reset x coordinate Integer None Clears the graphics win dow and sets the current location to the zx and y coordinate specified Program Algorithm Design This section examines each of the functions identified by the structural design and outlines an algo rithm for its implementation All algori
135. equencer will allow the user to input the details of various notes and then play them back in order Each note can be characterised by four pieces of information e pitch e channel e velocity e duration in milliseconds This information could be stored in a structure like the following typedef struct long_note_type int pitch int channel int velocity int duration note_type The project music3 contains the skeleton for the program you are about to write Copy the project and open it in the IDE Exercise 11 8 Using Structures for Music Write a program which prompts the user for the details required to play a number of notes pitch channel velocity duration You might like the user to be able to state how many notes they want to use although you will probably have to impose a maximum limit When the user has finished entering the information play the notes back to the user You might like to add a feature to allow the user to edit the details of the notes that they have already entered so that they may correct mistakes Exercise 11 9 Operating on the Sequence Alter your program so that the user may choose to play back the note sequence they have just recorded in a number of different ways e transposed up or down e in reverse order e the instrument s that is are being used Revision 1 3 Computer Programming Using C 159 Exercise 11 10 A More Advanced Sequencer
136. er Programming Using C 163 void change int i 4 i 20 Copies the value from argument variable j into parameter i int main void int 3 ls J 5 change j return 0 In the change function the value 20 is assigned to the parameter i Notice that the value of the variable j which only exists inside main is not affected ce change int i A A ee the value 20 into parameter i int main void int j j Ty main variable j unaffected change Jj return 0 When the change function returns the program flow to the main function the value of j has not changed void change int i i 20 int main void int j j j 5 Value of variable j has not changed change j return 0 This system of copying the value of an argument into the parameter is called passing by value It is the normal way in which C functions work It has a very good side and a less good side e the good side is that functions are not able to affect the code that calls them This stops them from damaging other parts of your program and ensures encapsulation this was mentioned in laboratory 5 e the less good side is that the only way to return a value is by using the return statement This limits a function to only returning one value Sometimes you might want to write code in which a function returns more than one value The next part of the lab introduces pointers which amongst other things allow us to get roun
137. er Programming Using C 31 Exercise 1 6 A First Look at Graphics Before we continue you should make sure that you understand what is happening in this graphics example Some things to investigate for yourself e try changing the colour that is used to plot the circle e try moving the position in which the circle is drawn by changing the coordinates e try changing the size of the circle After you have made a change remember to rebuild the program and execute it to see the results 1 7 2 Some Simple Drawing The next thing you will do is to draw a very simple stick person using a circle and four lines Hopefully it will look a bit like this You have already seen the circle function The only other function you need to know about to draw the stick person is the 1ine function Function Reference line Draws a line in the graphics window line start x start_y end_x end_y e g Lime 100 150 200 290 p The line function draws a line in the graphics window using the current colour The line is defined by its starting point and its ending point The arguments start_x and start_y define the x and y coordinates of the starting point respectively The arguments end_x and end y define the z and y coordinates of the ending point respectively line is defined in graphics 1ib h 32 Computer Programming Using C Revision 1 3 Exercise 1 7 Drawing the Stick Person Change the program to
138. er an integer number 40 Computer Programming Using C Revision 1 3 Wait for the user to enter a number and hit enter x x Store the number in the number_entered variable scanf Sd number_entered Display the number that the user entered x printf The number you entered was d n number_entered return 0 The program uses the printf function that you met in the last laboratory to display a message to the user printf Enter an integer number It then uses the scanf function to get a single integer value from the user and to put the information into the number_entered variable scanf Sd number_entered The first argument of the scanf function is at least one place holder enclosed in double quotes exactly the same as they are used in the printf function In a similar way to print for every place holder in the quotes there should be a variable listed as part of the function call Usually you will only use one place holder and one variable with scanf You should notice that the variable has an ampersand a s character before it This is not a mistake When you use scanf you should put an ampersand before each variable name The exact reason for this is quite complicated and you will learn about it in laboratory 12 next term Until then you will have to remember that whenever you use the scanf function to get numbers or single characters from the user you must put an ampersan
139. er presses an invalid key you should display an error message and not show the graphics window with the stick person in it The circle which makes up the head of the stick person is currently empty We can use the graphics function floodfill to fill this circle with colour The floodfill function pours colour onto the screen at a specified location The colour spreads out until it reaches a line of a colour that you specify If it doesn t meet a line with the colour you specify it will fill the whole screen You can control the pattern and the colour that is used for the fill with the set illstyle function This is very like the setcolor function it sets the style and colour to be used by all loodf il11 function calls Function Reference set f illstyle Sets the graphical style used for fill oper ations setfillstyle pattern_number colour_number e g setfillstyle SOLID_FILL RED The setfillstyle function determines the pattern and colour that is used for all future floodfill operations The pattern is set using the pattern_number argument The colour is set using the colour_number The pattern_number argument should be an integer number from 0 to 12 while colour_number should be an integer from 0 to 15 You can just pass it a number for either but the graphics systems defines some pattern names to make it easier to use O EMPTY_FILL
140. er should be able to specify an angle between 0 and 90 but not outside that range Use the sin and cos functions from the maths library to resolve the velocity into horizontal and vertical components Remember that the maths library functions expect the angle to be in radians You will need to convert the angle from degrees into radians 5 7 3 Making Your Program More Visually Appealing This section introduces three new graphics functions that you might find useful e the cleardevice function clears any drawing you have done from the graphics window just as if you had re opened the window e the setbkcolor function which sets the current background colour e the outtextxy function allows you to put text in the graphics window Function Reference cleardevice Clears the contents of the graphics win dow void cleardevice void The cleardevice function clears the graphics window of any contents It fills the screen with the current background colour previously set using setbkcolor and sets the current location which is used for things like 1ineto to 0 0 cleardevice is defined in graphics 1ib h Revision 1 3 Computer Programming Using C 99 Function Reference setbkcolor Sets the background colour void serokcolor inte Collec e The setbkcolor function sets the current background colour It takes one argument which is the integer number which identifies the colour You can use the same
141. ercise 12 8 Improving Program Efficiency Using Pointers When you pass a structure by value all of the member variables are copied into the parameter This can make your programs inefficient both in terms of their speed and the amount of memory they use Change the draw_line graphics option or the play_note music option function so that the structure is passed by reference rather than by value 12 6 Summary Now that you have finished this laboratory you should know that the usual way in which functions are called involves a copy of the values of the arguments into the function parameters and is called passing by value You should understand what a pointer is and be able to use the reference 8 and dereference opera tors to work with pointers The technique of using pointers as parameters to functions is called passing by reference you should know how to write and call functions which use this technique In the final part of the lab you used pointers with structures You should have met the gt operator which is designed for working with structures You should also have altered one of the programs you created in lab 11 so that it passed structures by reference 172 Computer Programming Using C Revision 1 3 Laboratory 13 Arrays and Strings Revisited and Allocating Memory 13 1 Overview In lab 12 you were introduced to pointers This lab begins by examining arrays showing that there is a strong relationship
142. es for Conditional Compilation In laboratory 2 we saw how to get parts of your program to execute only under certain conditions using an if statement There is a similar preprocessor directive that allows you to conditionally compile parts of your program under certain conditions Logically the directive is called if Close whatever project you have open Copy and open the lab4a project You should see that the code is very similar to the example we looked at in the first laboratory It has some additional lines at the end Revision 1 3 Computer Programming Using C 79 to display the results it also has this bit of code if defined DEBUG printf time_to_fly d time_to_drive d n time_to_fly time_to_drive endif What do you think this will do Try building and executing the program to find out gF Exercise 4 5 Investigating Conditional Compilation 1 Make the compiler ignore the line define DEBUG by enclosing it in a comment enclose it between and Build and execute the program What has happened You should have seen that the code inside if endif directives is only compiled under certain conditions The if directive allows you to set conditions under which parts of your program will be removed by the preprocessor and therefore ignored by the compiler For example if 0 endif will never compile the code between the if and endif directives because 0 is tre
143. et leave to be 1 end switch loop while leave is zero close the graphics window end function main Sos N N Gl Fl The main function always returns 0 The two other functions are considerably simpler The display_welcome function simply displays the welcome message and then waits for a key press The pseudo code is as follows begin function display_welcome wa 134 Computer Programming Using C Revision 1 3 display welcome messag call getch to wait for a key press end function display_welcome The display_welcome function has no variables or parameters The reset function takes two parameters Parameter Range C Type Description x 0 640 int The x coordinate that the drawing location should be set to y 0 480 int The y coordinate that the drawing location should be set to The reset function clears the graphics window and sets the current location to the z and y coordinate specified by the parameters The pseudo code is as follows begin function reset call cleardevice to clear graphics window call moveto passing x and y parameters end function reset The reset function has no variables This completes the design 8 3 3 Implementation You should now take the time to make sure that you understand how the design is proposing to solve the problem The pseudo code for the main function is quite complicated Have a think about how you are going to translate it in
144. evice Add as much to your program as you can using functions appropriately 5 8 Music Option Open your music2 project that have been working on in previous laboratories Your program should play a simple piece constructed of whole tone scales with appropriate drone tones and dynamics The piece should play until the user presses a key By now your code will be getting quite large so the first 100 Computer Programming Using C Revision 1 3 thing we will do is to split it into functions to make the program more readable and to allow code reuse Exercise 5 11 Splitting Your Program into Functions Define a function that produces a number of whole tone scales The function should have parameters for the number of scales to play the pitch of the starting note in the scale the number of notes in each scale e the velocity to use for the scales You can add other parameters if you want Place this function under the main function in your source file You will need to define a prototype for the function Currently your program repeats the same sequence of scales until the user presses a key We can make a music program more interesting by using randomness to try to create a program which improvises C contains standard functions for producing random numbers but they are not easy to use The music library contains a much simpler random number function called random_number Function Reference random
145. f my_integer is din xrefmy_integer 5 0x12345678 fiysnteger 0x89012345 0x12345678 ref_my_integer my_integer printf my_integer is now d n my_integer return 0 The assignment copies the value 5 into the location that is referenced by the pointer ref_my_integer which changes the my_integer variable The value that is displayed on the screen is therefore 5 demonstrators to explain it to you Exercise 12 3 More Pointer Investigation Try stepping through the lab12a program Watch the variables change in the watch window you may need to click on the tab marked locals to display both the variables Make sure that you understand what is happening before you continue If necessary ask one of the You can see that the reference amp and dereference x operators do opposite things e The reference operator amp creates a reference a pointer from a variable It take simply takes the address of the memory location the variable is using to store its information in e The dereference operator uses a reference to find the original variable It uses the address stored in the pointer variable to find the memory location containing the information 168 Computer Programming Using C Revision 1 3 Syntax Pointer Reference and Dereference Operators The reference operator amp operates on a variable to create a reference It does this by obtaining the address of the memory l
146. f A printf statement I have just added n What happens when you execute it You should find that the second printf statement is always executed Compare the code with the syntax box on if statements You should notice that i f and else clauses a clause is a part of a statement only guard one statement If you want the if statement to guard more than one statement you must group statements together into a compound statement A compound statement replaces any statement like this statement including the semicolon with a set of statements grouped together by braces curly brackets Like this statementl statement2 You can replace any statement in C with a compound statement This is useful for making an if state ment guard a set of statements Returning to our example it should be rewritten like this else PLINE fC wb printf A printf statement I have just added n Exercise 2 4 Adding Compound Statements Add an extra printf statement to every branch of your if else You will need to use a com pound statement for each branch Check that it works as you would expect when you execute it Compound statements are very useful for if statements You will find them essential in the next lab when we look at repeating and iterating sets of statements grouped together into block statements 46 Computer Programming Using C Revision 1 3 Syntax Compound Statements enteral A compound statement is a
147. f a double variable lf n a_double The printf function displays text and data on the screen It takes the following arguments e format_string is the text to be printed on the screen enclosed in double quotes e data_item these are variables whose values will be printed on the screen In order to specify where in the text the values of variables are to be printed special characters are used in format_string These are known as place holders because they reserve space for these values to be printed All print f place holders begin with a percent character The most common place holders are e Sd for integer int variables You can remember this as d for decimal e 1f real valued double variables e Sc for single characters char The place holders are matched with the comma separated data_item arguments in order For ex ample printf Result 1 d result 2 d n 6 7 will display Result 1 6 result 2 7 The printf function is defined in the header file stdio h therefore to use printf you must make sure that the line include lt stdio h gt appears near the top of your source file This allows the compiler to understand and find the printf function The printf format_st ring can also contain special sequences of characters such as n which begins a new line and t which displays a tab character The backslash functions as a special character causing the next character to be t
148. f another variable This kind of vari able is called a reference because instead of holding a value of its own it references another memory location which holds a value In C references are more commonly used pointers The two names are interchangeable we will most often use the name pointer in this lab script The diagram below shows a pointer variable called refmy integer which references the variable my_integer The reference is shown with an arrow 0x12345678 my integer y ref my integer is a pointer to my_integer 0x89012345 0x12345678 ref my integer Notice that the contents of the memory location associated with the pointer variable ref my integer is 0x12345678 This is the address of the memory location associated with the my_integer variable Pointers in C are declared like this int ref_my_integer This line declares a new variable called ref my_integer which is a pointer or a reference to an int Notice that we have specified what this point will reference an integer type int This pointer cannot be used to reference a double or a char or anything else This helps to prevent some simple program ming mistakes The star x is one of two C operators which are used when working with pointers the other is the ampersand amp You can think of these operators as travelling along the arrow which goes from a pointer to the memory location it is pointing to Revision 1 3 Computer Programming Using C 165 0x12345678 my int
149. ference s Using the s placeholder with scanf and printf scanf Slengths string_variable rca MS Sila VeL 9 The s placeholder allows scanf and printf to handle strings When using scanf it is good programming practice to make sure the length of the string that can be read is limited using a number length between the percentage sign and the s character This number should be one less than the length of the array to allow room for the null termination character As the argument which matches the s placeholder is an array It does not need to be preceded by an ampersand Revision 1 3 Computer Programming Using C 113 Exercise 6 4 Understanding Character Arrays Test the lab6b program with different input You should find that scanf prevents you from being able to enter nothing at all It also only ever uses the first word that you enter e Why is the scanf placeholder 319s Why is it not 320s e What happens if you enter a word longer than 19 characters e What happens if you change the placeholder to have a number less than 19 Exercise 6 5 Handling Null Terminated Strings Add to lab6b to create a function with the prototype int string_length char string The function should count the number of characters in the string It should stop counting when it reaches the null character It should be able to handle situations where there are no characters in the string i e the firs
150. ful not to try and access a value which is not really in the array In the context of stacks there are two situations which could potentially break this rule e if you attempt to add more items to the stack than the buffer array can hold this is called overflow 188 Computer Programming Using C Revision 1 3 e if you attempt to remove an item from the stack when the stack is empty this is called underflow Both of these situations could cause a program to malfunction or crash seriously Exercise 14 2 Handling Overflow and Underflow Conditions The lab14 program currently has no protection against overflow or underflow Make sure you trap these conditions so that they can never happen Warn the user if they attempt to add more data items than the stack will hold or if they try to remove data items when the stack is empty 14 5 Queues FIFO Buffers In section 14 3 of this lab the analogy of a set of building blocks was used to represent a LIFO buffer Each building block represented a data item You can imagine a FIFO buffer as a queue of people waiting to be served at a bar Each carries a sign with a number on it In this case the people in the queue with their signs represent the data items SS Queue The first person to join the queue at the bar will be the first person to be served this is a perfect world All of the people in the queue will be served in order as they reach the bar The first into the
151. g Using C 137 Start Each of the structural units in the diagram is a function These functions are documented in the table below display_keys Function Name Input Parameters Return Value Description main None Integer error level Driving function calls all passed to environ others always returns 0 ment display_welcome None None Displays the welcome message to the user display_keys None None Displays the instructions for how to use the key board to the user key to pitch key code Integer Integer the pitch of the note to play or zero if the key was Converts a key number to a pitch or to zero if the key wasn t valid or to 1 not valid or 1 if the program should exit if the key was q or Q and the program should exit The key to_pitch function translates a key numbers like that returned from get ch into a pitch If the key was not a valid note key it returns zero If the key was q or Q it returns 1 To allows these numbers to be easily read and recognised symbols should be defined for them as follows Symbol Name Value PITCH_INVALID 0 PITCH_QUIT 1 The main contains the main loop which keeps the program running Its most important role is to accept key presses from the user and then to call the key_to_pitch function to translate the key numbers into a pitch value It then reacts to the pitch num
152. gers It would be possible to store the two integers as strings but this would require conversions to store and retrieve the information This would be inefficient and error prone C structures allow us to collect information together in a very similar way to the cards mentioned above We can declare a structure using the struct keyword This is normally done in two stages e Firstly you use the struct keyword to define a template for the structure This is a bit like creating a card which has headings but has not been filled in yet The template is given a name so that you can refer to it e Once you have declared the template you can now use it To do this you specify the name of the template when declaring a variable in place of a type name like int or double We will look at each of these stages in turn To define the template you first specify the struct keyword followed by a tag which is the name of the template you are defining Following this in a set of curly braces you define one or more variables which are part of the structure These are called member variables A structure template definition for the details we want to store about a student is shown below Definition keyword a Structure type name or tag struct student_type char family_name 40 Ghar ge ven tiame 40 Member variables int year_of_birth int course_code he Remember that this does not actually declare a variable yet All we have done is decide
153. hand mouse button Then choose the Remove Breakpoint option from the menu Exercise 4 7 Trying Out the Breakpoint Feature Now is your opportunity to try out breakpoints Try setting them removing them and using them for debugging Breakpoints are very useful and you will probably find them invaluable when de bugging your programs for your assessments 4 7 Locating the Programs You Have Written All the programs you have produced so far do not have to be run in the IDE In fact they do not need the C source code or the C compiler to run once you have built them If you sent your program to a friend you would only have to send them one file the executable Just to prove this point you are now going to try executing some of your programs without using the IDE First close the IDE we won t be using it now Now we have to find the executable file that was built by the compiler and linker from your C source code Open up My Documents from the desktop and double click on the clab folder that you created in the first lab You should now see one folder for each project you have worked on Double click on the folder for the last option project you were working on either graphics1 or music2 depending on which option you are doing You should see some files and a folder called Debug Double click on the Debug folder to view its contents You will see one file which has the same name as the project
154. hat key was pressed using the getch if kbhit returned 1 kbhit is defined in conio h To use kbhit you should make sure that the line include lt conio h gt is at the top of your source file Revision 1 3 Computer Programming Using C 71 Exercise 3 14 Repeating Until a Key Is Pressed Alter your program to play the four sets of ascending whole tone scales repeatedly until the user presses a key When the key is pressed the program should finish its current group of four sets of scales and then finish with the descending scale You might like to add to the code which executes after the key is pressed to give the piece more of a finale 3 7 Summary Now that you have completed this lab you should have the ability to use three kinds of repetition structure e while loops e do while loops e for loops You should also be able to decide which of these types of loop is appropriate in a given situation If you completed the graphics option you should have made some major changes to your graphics program which allow your stick person to throw an object The path of the object should appear in the graphics window The user should be able to move the stick person left and right using the arrow keys and should have three goes at throwing an object If you completed the music option you should have investigated how to use loops to generate scales You should have put together a piece built on repetition of sim
155. he curly brackets are known as initialisers There must not be more initialisers that elements in the array The next program you will write will use initialisers to set numbers in an array The difference from the arrays we have just been looking at is that this next program will need a multidimensional array The arrays you have seen so far have a single dimension they work like a table with a single column The subscript is like the row number telling the program where to look in the table A two dimensional array has two subscripts it works like a table with multiple columns The two subscripts act as the row and column numbers selecting a single cell in the table Three and more dimensions are also possible A two dimensional array is declared in C like this int data_table 5 3 You could think of the dat a_t able array as being a table with 5 rows and 3 columns You would access the data_table array like this printf The first element in the table is d data_table 0 0 Notice that you need to specify both subscripts Initialising a two dimensional array is like treating each row as a one dimensional array and then col lecting all of the rows together Look at this example int data_table 5 3 1 1 2 3 12 3 4 13 4 5 14 9 6 5 6 7 y If we treat the first subscript as the column index and the second as the row index data_table is equivalent to the following table of values Ol H
156. he demonstrators for help 1 8 2 Playing More than One Note at Once If you turn two notes on one after the other they will both play at once For example midi_note pitch channel velocity midi_note pitch 3 channel velocity and after a pause turn the same notes off midi_note pitch channel 0 midi_note pitch 3 channel 0 36 Computer Programming Using C Revision 1 3 By choosing the correct notes you can create a chord For example you could turn on a major triad with the following code x Turn on the tonic x midi_note pitch channel velocity x Turn on the major third _note pitch 4 channel velocity 3 P Q H x Turn on the perfect fifth idi_note pitch 7 channel velocity 3 You would need to turn all the notes off again afterwards Exercise 1 9 Creating Chords Change your tune so that it ends on an appropriate major triad Experiment with ending on other chords can you produce e a minor chord e a dominant 7th e a diminished chord e a minor 7th added 9th chord Some of these may not be the most appropriate for your tune but try them anyway 1 8 3 Changing the Instrument You can change the MIDI instrument that is being used on a given channel using the program_change function For example program_change 1 57 sets MIDI channel 1 to use instrument number 57 which is usually a trumpet The exa
157. he end of the string A string that ends in a null character is said to be null terminated All strings in C are null terminated When you initialise a string the null termination is added to the array for you automatically Because the null termination takes up an extra character you must make sure that any character array you declare has one more space in it than the maximum number of characters that you want it to hold For example if you wanted to declare an array for holding strings of up to 20 characters you should declare it as char another_string 21 to make sure that there is room for the null termination character You can use the null termination to find the end of a string in an array For example you could check the first element in the array to detect whether a string is empty i e it has no characters like this You would check for the null termination like this if another_string 0 0 The string is empty else The string is not empty The example project lab6b contains an example of how to do some basic string handling Copy the gF lab6b project and open it in the IDE Try building and executing the project What does it do The source code for lab6b c is shown below A program to demonstrate strings x C Programming laboratory 6 x include lt stdio h gt x Program starts here int main void 112 Computer Programming Using C Revision 1
158. he pseudo code is as follows begin function display_welcome display Welcome to KeyNote display Press q to quit end function display_welcome The display welcome function has no variables or parameters The display_keys function displays the list of keys with their corresponding notes see earlier in the design begin function display_keys display list of keys and notes end function display_welcome The display keys function has no variables or parameters The key_to_pitch takes one parameter Parameter Range C Type Description key a A w W s S e int The number of the key that should be translated to E d D de E E IES a pitch E G y Y Y H w U 9 T kK KY g Q Other values should be handled as invalid The key to pitch also has one variable Variable Range C Type Description pitch 60 72 0 1 int The pitch of the note to play or zero if the note should not be played or 1 if the program should exit The way in which the key to pitch function works is very simple but quite long It simply recognises each of the valid key numbers and translates them to a pitch The pseudo code is shown below Revision 1 3 Computer Programming Using C 139 begin function key_to_pitch switch using key case a or A set pitch to be 60 case w or W set pitch to be
159. he user to choose the initial velocity of the object It should then display the stick person and allow them to use the arrow keys to move the stick person The program then waits for the user to press Enter before it plots the path of the projectile After the object has been thrown the program waits for a key press and then exits You should alter this process so that after this last key press the program allows the user to have another go providing they have not already had three goes You should close the graphics window and re open it for each go Hint You will have to put almost all of the code you already have inside another for loop to get this to work 68 Computer Programming Using C Revision 1 3 3 6 Music Option 3 6 1 Simple Scales Repetition is very important in music We are going to use loops to generate simple scales and use them to attempt to construct music in a minimalist style similar to that used by composers such as Steve Reich Terry Riley and Philip Glass The project music2 plays one octave of a chromatic scale starting on middle C Copy the project and open it The source code for music2 c is shown below x A program to demonstrate a simple chromatic scale x C Programming laboratory 3 x include midi_lib h int main void x Declare integer variables for specifying a note int pitch channel velocity offset Set the pitch variable to 60 which is middle C
160. hould help you when you come to write your own software reports There are two designs in this script one is for the graphics option the other is for the music option You should attempt the one you are most familiar with 8 3 Graphics Option This design takes the example of a simple piece of software intended to behave like a simple drawing device an Etch a Sketch 8 3 1 Specification The program is required to e allow the user to draw a line using the arrow keys e allow the user to clear the drawing and start again e drawing should start from the centre of the screen e allow the user to exit at any time Additionally it would be desirable if the program e ensures that the drawing does not leave the visible screen area e is easy and straightforward to use 8 3 2 Design The design will be split into three stages the user interface design a structural design and an algorithm design This process roughly corresponds to a top down design approach which starts from what the program should appear to do and works towards the question of how that functionality should be achieved User Interface Design The program will start by welcoming the user informing them how to use the program and then dis playing the graphics window in which they can draw Revision 1 3 Computer Programming Using C 131 At program start up the following text should be displayed Welcome to SketchPad Arrow keys let you draw P
161. ide a loop you could add an if statement that displays the value after the tenth iteration The code could be removed from the final program by ensuring that you do not define a DEBUG tag 4 6 Using Breakpoints for Debugging Right from the beginning of this course we have used the IDE s debugging facility for stepping through your programs If you are confident that all of the code at the beginning of you program works then stepping through it to get to the bit you are worried about can be very boring If you have loops with a large number of iterations then it could take all day Revision 1 3 Computer Programming Using C 81 Fortunately the debugger has a facility for you to be able to specify a line in your source code that you want to be able to stop on To do this you mark a line in your code with a breakpoint Open a project you have been working on in previous labs Choose something with a fairly substantial SP amount of code in it a project from your option either graphics or music would be a good idea Pick a line of source code that will execute i e not a comment and click on it with the right hand mouse button You should see as menu like this one e some variables for the calculat ne Lc 00 Gu tc Ea Copy us mn Paste e Insert File into Project st Open Document tc Ec EE List Members jee R Type Info Pl Parameter Info EE act Complete Word At il Go To Definition Of distanc _t
162. ike this ifndef GRAPH_FUN_H If the label has not been defined then the preprocessor will continue reading the contents of the file To make sure that the file does not get processed again the first thing we do is define the label using the define directive like this define GRAPH _FUN_H At the end of the source file we must include a endif directive to match the ifndef directive like this endif Now that the compiler has seen the contents of the header file once the label _ GRAPH_FUN_H__ has been defined If the header file is included again the compiler will reach the line ifndef GRAPH_FUN_H where it will find that the label _GRAPH_FUN_H__ has already been defined It will therefore skip to the endif directive at the end of the source file So the contents of the header are only processed once no matter how many times the file is included The example header file that we looked at earlier graph_fun h should look like this x Header file for graph_fun c Function prototypes only ifndef GRAPH_FUN_H define GRAPH_FUN_H void show_hello void void draw_stick_person int x int y void draw_throw int x int y double velocity endif This system of protection made up of a define directive a ifndef directive and a tendi f directive is called a sentry Exercise 7 4 Adding Sentries to Your Header Files Make sure you understand how sentries work and why the
163. ile graphics1 c which uses the functions show_hello draw_stick_ person and draw _throw the header file must be included with the line include graph_fun h There is now no need to put any prototypes for the functions show_hello draw_stick_person and draw_throw in graphics1 c If we wished to use any of these functions in another file we would simply put the include directive at the top of the file You will remember from laboratory 4 that the include directive just includes the source from the file that is named into the current file In this case it is used to make sure that prototypes for the functions in graph fun c are included wherever they might be used Creating a new header file is very similar to creating a new source file Choose New from the File menu graphics1 Microsoft Visual C The New file dialog box will appear just as when creating a new source file 124 Computer Programming Using C Revision 1 3 si Files Projects Workspaces Other Documents Select C C Header File 44 Active Server Page JV Add to project el Binary File oraphics1 y 45 Bitmap File E C C Header File 2 C Source File File name at Cursor File graph_fun h S HTML Page Icon File Location qu Macro File H clab graphics1 E 5 Resource Script E Resource Template Text File Cancel Type the name of your new file To create you
164. ile is shown below g x A Program to Demonstrate Recursion Lab 18 x include lt stdio h gt x Sums all the numbers between start and end x start must be smaller than end x int sum_series int start int end If there is no difference between the start and end numbers there is nothing to sum if start end return end Add the current start number to all the other numbers in the series x return start sum_series start 1 end Requests two numbers from the user and displays the x sum of all the integer numbers in between int main void int start end sum x Ask the user for numbers x printf Please enter two integer numbers n printf The first number must be smaller than the second n printf First number scanf Sd start printf Second number scanf Sd send x Calculate the sum of the series sum sum_series start end Display the result printf The sum of all the integers from d to d is d n start end sum return 0 This program uses recursion to calculate the sum of all the integers from one number to another includ ing the numbers themselves For example the sum of all the numbers from 1 to 5 is 1 2 3 4 5 15 This sum is calculated by the sum_series function You will notice from the source code above that the sum_series function calls itself It uses recursion to loop through the nu
165. ill need it in lab 18 Exercise 17 4 Reading Multiple Numbers from a File The lab17a project is a nearly empty template for this exercise copy the project and open it in the IDE Write a program that opens the file that was to written by the program in Exercise 17 3 It should read 20 numbers from this file into an array At the end of the program it should display the numbers Revision 1 3 Computer Programming Using C 219 Exercise 17 5 Making the Read Operation More Flexible The lab17a program you have just written depends on there being 20 numbers in the file it is reading from If there are more than that the numbers do not get read If there are fewer there will be a problem In this case the scanf function will return the constant EOF which stands for End Of File Alter the lab17a program so that it will read any amount of numbers in from a file The numbers should be read into an array the memory for which is dynamically allocated using malloc To do this you will need to read the file twice e once to determine how many numbers there are in the file so that you can allocate the array e a second time to read the numbers into the array You will need this program when you come to attempt some of the exercises in laboratory 18 17 5 File Operations with Structures The examples we have looked at so far have only written or read a single number with each fprintf an
166. iming to gather information so that you can put together a concrete specification for what the software should do The main things you should be concerned with in an analysis are e The inputs to the problem including units and expected range e The outputs the solution will have to produce including units and expected range e What kind of screen output is implied by the specification will it be graphics or text e What size screen especially for graphics is reasonable on your platform What is the available range of midi notes channels All formulae your program will use including calculation formulae and others such as physics tempo conversion etc State how the results of your program will appear sound in general terms e Who is your user What are their needs Are they technically or musically literate Are they computer literate As a general rule of thumb it shouldn t matter that you are going to implement your program in C The design should be independent of programming language This means that it should not contain C terms like int double or functions like scanf or midi_note Be careful not to begin your design in your analysis You cannot begin a design until you have a formal specification 8 5 3 Specification You should use your analysis to put together a list of exactly what your program needs to do Itis very useful if you split this list into things that your program must do and what it would be desirable if
167. in bounds which you have specified For the next step you will need to make sure that all of the notes in the tune are specified as an offset Revision 1 3 Computer Programming Using C 55 from a variable whose value specifies the key For example int key The key of this piece is C All notes are specified with reference to middle C key 60 x Turn a note on x midi_note key 3 1 64 pause 1000 x Turn the note off x midi_note key 3 1 0 Ask a demonstrator for help if you do not understand how to do this Exercise 2 12 Adding User Control of Key The next step is to allow the user to choose the key in which the piece is played You should do this by showing the user a menu a list of possible keys Next to each choice you should indicate which keyboard key the user will need to press in order to select the musical key for the piece You may like to choose keys on the keyboard whose layout most closely resembles a standard piano style keyboard This choice should be case insensitive i e r and R should be treated the same You will probably want to use a switch statement for this You should use the default clause to watch for invalid input from the user If the user presses an invalid key you should display an error message and not play the tune 2 10 Summary Now that you have completed this lab you should have the ability to write conditional statements in C Y
168. in the section g Before You Begin These are e mapping your N drive e creating a folder called clab for your work For this lab we will be using the project lab1 Following the instructions in the section Before You Begin copy the project to your clab folder e open the IDE e open the project in the IDE If you have any questions about any of this steps just ask the demonstrators 14 Computer Programming Using C Revision 1 3 1 3 Introducing the IDE This laboratory course uses Microsoft Visual C Version 6 0 Although the software supports program ming in the C language as well as the C language we will just be using C We will be using Microsoft Visual Studio to create programs using Microsoft Visual C This software is called an Integrated Devel opment Environment or IDE because it combines things that many years ago used to be separate They are e an editor which allows you to edit the text files that contain the C language which will become your program these are often known as source files e a compiler which takes the source files and translates them from text in the C language to machine code which the computer can understand and execute All programs on your computer are in machine code This is all you need to create a program in C but an IDE also usually contains e a debugger which allows you to test out your programs in a very controlled way and diagnose proble
169. ing in the C program source code e What do you think the program is trying to do e Repeat the calculations with a calculator What results do you get Write them down as we will need them very shortly e When you compile and run the program what do you think it will appear to do If you can t answer these questions ask one of the demonstrators for help 1 5 Compiling Executing and Debugging a C Program We are now going to use the IDE to compile execute run and debug the C program we have just been looking at First we will look at how to compile a program using the IDE Compiling a program happens in two stages e compiling where each source file is translated into an intermediate format called an object file e linking where all the object files are linked together to form a single machine code file an executable On Microsoft Windows all executables end with the letters exe The commands for instructing the IDE to compile your project are on the Build menu abic ee aject Build Tools Window Help 3 compile lab1 c Ctrl F m Build lab1 exe All alc es Rebuild All ajx Batch Build fs Clean Start Debug Debugger Remote Connection tk Execute lab1 exe Ctrl FS Set Active Configuration Configurations Profile int average_speed Let us look at the top three menu items Pw f 20 Computer Programming Using C Revision 1 3
170. ing into the Middle of the List When adding to the middle of the list there is a structure before the point of insertion and there is a structure after it This is shown in the diagram below the new structure is shown shaded and is not yet linked into the list Revision 1 3 Computer Programming Using C 209 aa ae _ gt ENN 7 a lt We ee gt e its next pointer is the same as the next pointer of the structure before it in the list The new structure must be set so that e its previous pointer is the same as the previous pointer of the structure after it in the list This is shown below GAR rn E lt gt Structure The previous pointer of the structure which is next on the list must be set to reference the new structure a scr o src ES a src Finally the next pointer of the structure after the new structure on the list must be set to reference the new structure Soe sie secure de Seco The structure has been successfully added to the middle of the list Adding to an Empty List Adding to an empty list is a simple operation To begin with both the first pointer and the last pointer will be set to NULL 210 Computer Programming Using C Revision 1 3 First Pointer Last Pointer gt NULL NULL The next pointer and previous pointer of the new structure should both be set to be NULL First Pointer La
171. ion prototypes will be used in all function boxes from now on You should understand how to use the f 1ush function to control the way scanf works and to ensure that user input is validated correctly In the second part of the lab you were introduced to some more mathematical functions which you might find useful In the graphics option you had to put your knowledge of functions into practice and you improved your program to allow the user to choose the launch angle for the projectile In the music option you were introduced to the random_number function which you used to try to produce a program which improvises and found out how hard it is to get it to sound musical 102 Computer Programming Using C Revision 1 3 Laboratory 6 Atrays and Strings 6 1 Overview This laboratory introduces you to arrays which are a way to create a variable that has the capacity to store many values Each of the values in the array can be accessed by using an index You will learn how to create and use arrays and how to make sure that they are initialised with specific values when your program starts You will also learn about multidimensional arrays which can be used to store data in a similar way to tables You have already been using text enclosed in quotation marks In this laboratory you will be learn more about these text or character strings which are actually a special form of array You will learn how to create and manipulate them I
172. isually Appealing 98 9 8 MUSIC OpPHON ie ama dea ek dee Dale Sib ed O e Su aa od ods 99 9 9 GUMMA Yee 9b 08 tical RRA RNA 101 Arrays and Strings 103 OL ONCE Wi Rota ice So Rk EO Gt ee ee As ES he 103 6 2 Introducing Arrays gt ice we A Moe Peele O42 be ee 103 6 3 Working with Arrays 1 ees 105 6 4 Initialising Arrays and Multi Dimensional Arrays 2 2 0 ooo o 108 6 5 Strings A Special Kind of Array 2 0 ees 110 6 6 Forming Strings Using sprintf sci eese apa ee ee 113 6 7 Graphics Option 2 S084 be ee a Oa de ee ye E a ee Da 115 6 8 Music OpHon soa gk he tt e ee Ra ds 116 6 9 Summary a ea Msi as aod aed tle at GE ee PRA Bo Yost Sik Dare ook AA alk 118 Structuring a Software Project 119 Fil CONCE Wii ae ne a heed ak he es Sh WR Ae et AR eo ee amp de ts 119 7 2 Splitting Your Program into Multiple Files 0 0 0 0 0000000 119 7 3 Creating Your Own Header Files ooo es 122 7 4 Protecting Your Header Files o oo o e 124 7 5 Good Programming Practice Some More Tips o ooo ooo o o 126 ASS II A OR 127 Practical Software Design 129 Sil OVERVIEWS oii ak oral dl a a ae eat Bee A et Sas 129 8 2 The Structure of Software Projects 2 0 aa 129 8 3 Graphics Option lt 00000 es Se ce ee A ee ee ee A 130 8 3 1 SpecificatOn ec ie ke doe aed GE A kg DA a ele See Bee 130 83 2 Desi sh sche al orev beta and
173. it Paste for this Try building the project What errors warnings do you get Why do you think there is a problem with putting functions in this order When a compiler is turning your source code into machine code it reads it in order When it reaches a function call it will try and associate it with a function that it already knows something about If it doesn t know anything about the function yet it has two options e make some assumptions about the information it doesn t know and continue assuming that the assumptions are correct e throw its hands up in the air and stop In most cases compilers choose the first of these options even though the second would cause fewer problems If the compiler subsequently finds some actual information about the function it usually discovers that the information it assumed was wrong which causes another problem The only information the compiler needs to know about a function to allow you to call it is e what arguments the function takes and what their types should be e what the return type of the function is These two pieces of information are both contained in the function head C provides a way to declare just the head of a function so that you can use it before you define the body of the function This allows you to put the function definition the combination of the head and the body below the place where it is called in the source code Declaring just the head of a
174. ite Operations 2 0 ooo e e o 214 17 4 Reading and Writing Many Lines to from a File ooo oo 217 17 5 File Operations with Structures 2 ooo o 219 17 6 SUM MALY tna segs Rae ee Oe a Aai es Pee ADT A 220 Sorting Searching and Recursion 221 1B KM OVeRVICW a ives led cos de Ee Loe hd on Ape iia ms ee a J te i 221 18 2 Sorting Data Using a Bubble Sort 2 aa 221 18 3 Introducing Recursion s ee 222 18 4 Searching Using Recursion 2 s ooo 224 TES SUMMAE T e ii leek na a Rane ring dew Teh et Ad Bit us hae eA ht eR 224 Summer Term Laboratory Outline 225 AT Overview 2 4 05 ho ate SO wee a 225 Suggested Further Reading 227 BA Tutorial Material 3 0 4 ee ea es ee Bae he A Me a ee o a at 227 B 2 Reference Material ee 227 Function Reference A Function Which does something o ooo o 2 printf Displays text onthe screen 2 ee 24 initwindow Creates a graphics window of a specified size 2 2 eee ee 28 setcolor Sets the current drawing colour 2 ee 29 circle Draws a circle in the graphics window 1 2 ooo ee 29 getch Waits for a key press from the keyboard 2 2 000000 cee ee een 30 closegraph Closes the graphics window 2 2 2 ee 30 line Draws a line in the graphics window 2 2 ee 31 midi_note Starts or stops a MIDI note playing o o o e 34 pause Waits for a sp
175. ius they entered using PI e display the result Exercise 4 2 Problems with define Directives You are now going to change the define PI directive so that it is wrong Change the line to be something like this define PI error 3 14159265 error This means that the text that will be substituted for the tag PI will be error 3 14159265 error which is obviously not going to be valid C Try compiling your program The compiler will give you an error message Which line does the compiler think the error is on Why is this If you don t understand this ask one of the demonstrators to explain it to you Remember to put the define directive back to how was before you continue Choose one of the following two exercises depending on which option you have been doing 78 Computer Programming Using C Revision 1 3 Exercise 4 3 Adding a define Directive Graphics Option Open the graphics program you have been working on which should be called graphics1 The horizontal location of the stick person is controlled by the user The vertical location is fixed Use define directives to define tags for e the width and height of the graphics window You could call these something like WINDOW_HEIGHT and WINDOW_WIDTH e the vertical location of the stick person You could call this something like PERSON_POS_Y e the key number for the Enter key 13 You could call this something like ENTER_KEY
176. key press getch 30 Computer Programming Using C Revision 1 3 This simply has the effect of leaving the graphics window on the screen while the computer waits for a key press When the user presses a key the program moves on and closes the graphics window Without this line the graphics window would disappear before you had a chance to see it We will be seeing more of the get ch function in later labs Function Reference getch Waits for a key press from the keyboard character getch The get ch function waits for a key press on the keyboard and then returns the value of the key that was pressed as an integer character code It is easy to use as a function that waits for a key press when you don t care about which key the user has pressed For example getch If you want to find out what key was pressed then you can assign the result of the function call to a variable int_variable getch We will see more of this in later labs getch is defined in conio h and also graphics_lib h After the user has pressed a key the program will continue to the next line closegraph which closes the graphics window Function Reference closegraph Closes the graphics window closegraph The closegraph function closes the graphics window It should be called before your program ends if you opened a graphics window closegraph is defined in graphics_lib h Revision 1 3 Comput
177. king Your Implementation Test your implementation to make sure that it works Does it do what you expected it to Try out an implementation that a friend has done you could let them try yours How similar is it If it is different why is it different If a design is good then different implementations of it should be indistinguishable to a user Do you think the design could be improved If so how 8 4 4 Extending the Design You now have the chance to add to the design Although you are not producing a software report for this program you should make some notes as if you were writing a proper design This gives you the chance to practice writing a small part of a design Exercise 8 7 Adding to the Design Imagine that the specification contained an extra point The program is required to e allow the user to change the volume at which the notes are played using the up and down arrow keys Make notes on how you would amend the design to meet this new part of the specification Make sure that each decision you take is fully justified Exercise 8 8 Implementing Your Design Addition Follow your design and implement the additions you have just made How easy is it to follow your design Are you having to correct design mistakes whilst you program Do you think that you missed anything in your design 8 5 Writing Your Own Report This section contains some very brief tips to help you write your own soft
178. l start by welcoming the user and informing them how to use the program The pro gram will then play notes in response to key presses until the user requests that the program should exit by pressing the q key At program start up the following text should be displayed Welcome to KeyNot Press a to quit The keyboard is the following keys a Cc w C s D e Eb d E f F Elre g G y G h A u Bb J B kJ The program should then wait for a key press When the user presses a key that is part of the list displayed the corresponding note should play for half a second 500ms To allow this duration to be changed easily it should be defined as a symbol Symbol Name Value NOTE_DURATION 500 For example when a user presses the a key a middle C should be played for half a second When the user presses the t key the F above middle C should be played for half a second All key presses should be case insensitive i e a and A should be treated identically If the user presses the q key the program should end Program Structure Design The program can be split up into separate functions corresponding to the different tasks the program must perform Separate functions are used for programming clarity and to enable code reuse The structure of the program is shown in the diagram below Revision 1 3 Computer Programmin
179. l styles 2 9 Music Option We are going to alter the MIDI program you were working on in the last laboratory to incorporate some of the new techniques you have just learned Close any project you have open at the moment and open the musicl project you were working on Your code from last lab should play a melody with some chords on a separate channel and a different instrument You are going to add to this program to allow the user to choose the instruments for the melody and backing chords You will also allow them to choose the key that the piece will be played in Exercise 2 11 Adding User Control of Instruments When your program starts the user should be able to type in a number which specifies the instrument that will be used to play the melody This should be a number from the General MIDI specification i e a number from 1 to 128 You should use an if statement to check that the number is in this range If the user does specify an invalid instrument number you should display an error message and not play the tune The process of ensuring that input is suitable for your program is known as input validation The program should do the same for the instrument which plays the chords i e the user should be able to choose an instrument for both before the piece is played You should now have a working program that allows the user to control the instruments that are used for both the melody and the chords with
180. l to The result of a relational expression is therefore true or false We say the expression evaluates to true or false So for example let s construct a relational expression which tests the value of a variable called test against the number 5 If test has the value 6 then e test lt 5 will evaluate to false e test gt 5 will evaluate to true e test 5 will evaluate to false e test 5 will evaluate to true If test has the value 5 then e test lt 5 will evaluate to false e test gt 5 will evaluate to false e test 5 will evaluate to true e test 5 will evaluate to false e test lt 5 will evaluate to true e test gt 5 will evaluate to true It is very important to notice that the operator for testing whether two things are the same is not This is the assignment operator which we saw in the previous lab The operator for testing if two things are the same is the double equals this is different to the assignment operator Don t get them confused Sometimes the compiler won t pick the error up and your program will malfunction in peculiar ways 44 Computer Programming Using C Revision 1 3 Syntax if statements if relational expression statement1 else statement2 The if statement allows you to execute a piece of your program conditionally The if statement guards a single statement statement1 of a program and only executes it if the relational_expression evaluates to true
181. lab3a The for loop is for count number_entered count lt 10 count printf Sd n count We can translate this directly to a while loop It then becomes count number_entered while count lt 10 printf d n count count which is very similar to the kinds of while loops that you have already seen and created for yourself except for the line count This line uses an operator you have not seen before called the post increment operator This is one of a number of shorthand operators in C The shorthand operators just make it easier to type and describe commonly used operations The post increment operator variable is equivalent to variable variable 1 i e the post increment operator simply adds one to a variable There is another way of writing the add one to a variable operation the pre increment operator The pre increment operator is used like this variable When used on its own like this there is no difference between the pre and post increment operators The difference between the two increment operators only becomes clear when you try and use an incre ment operator at the same time as doing something else 62 Computer Programming Using C Revision 1 3 Exercise 3 3 Understanding Pre and Post Increment Operators Temporarily add the following two lines of code to the end of the lab3a source code count 5 printf count d n coun
182. lent to adding one to a variable The decrement operator is equivalent to subtracting one from a variable The value of a post incremented expression is the value of the variable before it is incremented The value of a pre incremented expression is the value of the variable after it is incremented The same applies to the decrement operator Other shorthand operators are more straight forward e variablel variable2 is equivalent to variablel variablel variable2 e variablel variable2 is equivalent to variablel variablel variable2 variable2 is equivalent to variablel variable2 e variablel variablel Ss variable2 is equivalent to variablel variable2 e variablel variablel So for example COLI w Sip is directly equivalent to COU RCON 3 5 Exercise 3 5 Using a for Loop A More Advanced Problem Alter the lab3a source code so that after the user has entered a number the program responds by displaying the factorial x of the number that the user entered You should find that a for loop is the best way to do this Make sure your code still works if the user enters a number less than 1 Hint A factorial is the product of an integer and all positive integers below it e g 5 5 x 4 x 3 x 2x1 120 If you don t understand how to do this ask one of the demonstrators for help 64 Computer Programming Using C Revision 1 3 3 4 Deciding What Kind of Loop to Use There
183. lly an array looks like this 104 Computer Programming Using C Revision 1 3 This shows that one variable name identifies multiple spaces in the computer s memory These spaces are more properly called elements To identify which element we are talking about we reference it by number In C elements are numbered from zero This element number is called a subscript or an index A subscript is placed after the variable name in square brackets like this my_array 3 We can show the way that subscripts work on a diagram my array 1 my_array 3 Obviously the subscript must be an integer it wouldn t make sense to ask for element number 2 3859 You declare an array by specifying how many elements you want in that array For example int my_array 4 declares a new array variable called my_array Each element in the array contains an integer value The array has four elements in it Note that the last element is called my_array 3 Try to remember that when you are declaring an array the number in the square brackets is the number of elements not the subscript of the last element The subscript of the last element will be the size of the array minus one Syntax Array Declarations type name size more variable delcarations e g int an_integer_array 10 double a_real_array 6 int an_int_variable an_int_array 22 Arrays are variables which have space for more than one value The number of values that
184. lt square n This line calls the square function passing it the value of the argument n The square function has a return value which is equal to the square of the value of its argument in this case the return value is assigned to the result variable The code before the main function defines the display_welcome and squared functions The follow ing code defines the di splay welcome function void display_welcome void printf Welcome to the squaring numbers program n n A C function is made up of two parts e the first line is the function head and identifies the function We will study this part in more detail in the next section e the function body which is a set of statements enclosed in braces in exactly the same way as a compound statement The following code defines the square function int square int value int squared_value squared_value value value 90 Computer Programming Using C Revision 1 3 return squared_value Exercise 5 1 Investigating Functions Step through the lab5 program in the debugger Make sure you use the step into the F11 key feature to move the execution point into the functions when they are called e What happens to the variables defined in main when the execution point is inside the body of display welcome e What about when the execution point is inside the body of squared e What variables are available when the execution point is inside these fun
185. ly In general the array notation using the square bracketed subscript is much clearer and easier to read than pointer arithmetic Use pointer arithmetic very carefully try and avoid it if possible there are usually clearer ways to write the same thing The fact that arrays are just pointers with some memory attached is often reflected in functions which accept arrays as parameters In lab 6 you used a mean function to calculate the mean of an array of values The prototype for this function was double mean double values int num_values This prototype could equally have been written using pointer notation as double mean double values int num_values The two prototypes are effectively identical The body of the mean function used the square bracket notation for accessing the values parameter as an array Like this mean values current_value Revision 1 3 Computer Programming Using C 175 Even with the function prototype that declares the values parameter as a pointer this line does not need to be changed Just as an array variable is actually a pointer it is perfectly legitimate to treat a pointer as an array If you look at other people s code including standard C functions you will find that the pointer notation for array parameters to functions is very common Exercise 13 1 Investigating Arrays as Pointers When you pass an array to a function you are passing a pointer You can think of arra
186. mbers in the series 224 Computer Programming Using C Revision 1 3 Exercise 18 3 Investigating Recursion Try building and executing the lab18 program Try putting different combinations of numbers in and check the results the program will break if you put a large number in first Try stepping through the program and watching the contents of the variables change Make sure you understand how the program works Exercise 18 4 Calculating a Factorial Recursively In the lab3a program you wrote a program which calculated the factorial of a number using a for loop Change this program or write a new one so that it calculates the factorial of the number using a recursive function 18 4 Searching Using Recursion You have been taught about binary searches in your lectures A binary search looks for a particular item in a sorted list by repeatedly breaking the list down into two parts Exercise 18 5 A Recursive Binary Search Alter the lab17a program so that after it has sorted the list of numbers it asks the user for a number to search for It should then perform a binary search using a recursive search function to find the number The program should tell the user the line number of the number they requested in the sorted txt file This is the same as its index in the array 18 5 Summary Now that you have finished this laboratory you should understand how to implement a bubble s
187. ment This decision should be based on what each of the functions you have written do Some things to think about e You could collect together into one file the functions which interact with the user e If the main function is very complicated you might want to leave it in a file on its own e You might want to collect the graphics music functions together into one file Don t make things more complicated than necessary try to create a structure which is logical and would help someone else understand your program Decide on names for your files which reflect what they do To keep things simple it is best to avoid file names that have spaces in Make some notes about your file structure to help you remember your decisions You can now create a new file in which to place some of your code Select the New item from the File menu graphics1 Microsoft Visual C e Edit view Insert Project Buid TT ME Ctrl 0 Close oe Ma The New file dialog box will appear it is shown below 21xi Files Projects Workspaces Other Documents Select C Source File g Active Server Page IM Add to project H Binary File oraphics1 y 4 Bitmap File E C C Header File C Source File File name E Cursor File oraph tund 9 HTML Page Icon File Location 5 Macro File HAclabigraphics1 il 5 Resource Script 25 Resource Template Text File Cancel Type the
188. moveto Sets the current graphics location moveto x_position y position e g moveto 100 200 The graphics system keeps track of a current position which will be used by functions like lineto The moveto function allows you to set this current position When you call the moveto the current position is set to the value x_position y_position in graphics window coordinates Both of these values should be integers moveto is defined in graphics_lib h Function Reference lineto Draws a line from the current location to the specified location lineto x_position y_position e g limeco 1390 250 The graphics system keeps track of a current position which can be set by the moveto function The lineto function draws a line in the graphics window from the coordinates specified by the current position to the coordinates x_position y position These values must be integers Once the 1ineto function has drawn the line it sets the current position to be the end of the line it has drawn i e to coordinates x_position y_position The next time you call lineto it will draw from this point lineto is defined in graphics_lib h If you use the C code we have just looked at to calculate the y position of the object for a given x position we can use the 1ineto function for joining these points together with graphical lines Ina moment you are going to do this but firs
189. mple graphical operations x C Programming laboratory 1 x This line allows the compiler to understand the x graphics functions x include graphics_lib h Vx x The main function the program starts executing here int main void Declare two variables for the x and y positions x int x_position y_position Revision 1 3 Computer Programming Using C 27 x Open a graphics window x Make it 640 pixels wide by 480 pixels high x initwindow 640 480 Set up some coordinates x x_position 100 y_position 340 x Set the current drawing colour to be red setcolor RED x Draw a circle at the coordinates x Give it a radius of 10 pixels x circle x_position y_position 10 x Wait for a key press x getch Close the graphics window x closegraph return 0 We will go through this program a few lines at a time Make sure you understand it before continuing At the top of the source file after the initial comment is the line include graphics_lib h This allows the compiler to understand the graphics functions This works in the same way as the include lt stdio h gt line you needed to put into your code to allow the compiler to understand the printf function The first line of the main function declares two integer variables int x_position y_position These variables are declared in exactly the same way as in the first example The next line
190. ms Laboratory 7 Structuring a Software Project 7 1 Overview This laboratory introduces good programming practice for structuring software projects As your pro grams grow you will find that it is useful to split the functions you write across multiple source files This laboratory teaches you the best way to do this Although the concepts that are introduced in this lab will not have an effect on how your programs look once they are built well structured source code is important By using multiple files you can make your programs easier to understand and debug You can also make it easier to reuse code you create for one program when you are writing another Something which could save you a lot of effort Finally a few tips on good programming practice are covered Focussing on how to use indentation to make your programs more readable and how to use the IDE to do this easily 7 2 Splitting Your Program into Multiple Files In laboratory 6 you learned how and why to split your programs into functions One of the most important effects of splitting your code into functions is to wrap it up or encapsulate it into small chunks which can be reused easily To be able to reuse your function in another program you have had to copy it and paste it into another source file It is usual for more complicated C programs to be made up of more than one source file Each source file typically contains multiple functions The reasons for doing this
191. ms with them We will be making a great deal of use of all of these features right from the start The Visual Studio IDE you have in front of you should look something like this lab1 Microsoft Visual C ES Edit View Insert Project Build Tools Window Help a js ua ea jo e mare aj lle ce All global members Xr lle EN ly alx Hes Workspace lab1 1 project s lab1 files Source Files 2 labl c Header Files Resource Files Source Files FileView Tab Output Window Ma ClassView af Y DAN Build Debug Find in Files 1 Find in Files2 _ Ready The C language source files that make up the program are shown in the left pane In this example there is only one source file however projects may contain many source files If you can t see a source file list similar to the one shown above click the FileView tab When we perform tasks such as compiling or debugging programs the IDE will sometimes give you messages such as errors These will be shown in the output window If the IDE behaves in a way that you didn t expect this pane is a good place to look at first 1 4 Looking at Your First C Program SP Double click on the icon for the source file lab1 c Revision 1 3 Computer Programming Using C 15 sl labi tes 3 3 Source Files i RE E labl c i seven FA Header Files The C language source code will appear in the editor window This should lo
192. n the graphics option you will make use of arrays to make your graphics program more like a computer game In the music option you will find that arrays are very useful for defining musical relationships like the pitch relationships between notes in a scale 6 2 Introducing Arrays The variables you have been working with so far are a bit like scalar values in maths This laboratory is about arrays which are more like mathematical vectors Each variable you declare defines a space in the computer s memory in which you can store one value of the correct type We often show this as a diagram like this int my_integer 20 my integer The variable declaration on the left is equivalent to the diagram on the right In the diagram the box represents the space in the computer s memory in which the value of the variable is stored In this case you can see that the box contains the value 20 to indicate that the variable is assigned the value 20 The text to the right of the box my_integer identifies the name of the variable it provides a name for that space in the computer s memory Every variable you declare has a space in memory and the name of that variable identifies the memory space An array allows you to reserve more than one memory space for a single variable All the memory spaces you reserve will have the same type for example int When you use the variable you have to specify which one of the spaces you wish to access Diagrammatica
193. n to zero mean 0 Calculate the sum of all of the values for current_value 0 current_value lt num_values current_value mean values current_value x Divide by the number of values if there are any if num_values gt 0 mean num_values return mean The program uses the main function to collect information from the user It defines two other functions the welcome_message function displays useful text to the user when the program starts the mean function calculates the mean of the values that the user has entered The program will accept up to 10 data values so it declares an array of 10 double elements like this double data_values 10 The program allows the user to enter less than ten values if they want so we need to keep track of how many values they have entered This is done using another variable int num_data_values Revision 1 3 Computer Programming Using C 107 After the welcome message has been displayed the program enters a for loop This loop counts through the elements in the data_ values array Each time the loop runs each iteration the user is asked for a height The scanf function call places the result into the correct element in the array scanf Slf amp data_values curr_data_value This scanf call is just like the ones you have seen in previous labs except that instead of a scalar variable this call puts the result into an element of the array The eleme
194. nal expressions which evaluate to be either true or false and allow if statements to work You will find that switch statements are useful when there are lots of exact options This lab will also introduce you to two ways in which you can get input from the user of your program even if that s you The scanf function allows you to get a whole line of input from the user and is useful for obtaining input made up of lots of key presses like numbers The get ch function allows you to get a single key press from the user and is useful for more interactive input You will use both of these functions a great deal more in later labs as well 2 2 Getting Input from the User We will begin by using the scanf function to obtain input from the user of your program Copy the project lab2 and open it in the IDE The lab2 program will ask the user for an integer number After the user has typed in a number and pressed the Enter key the program tells the user what number they entered Try building and executing the lab2 project The source code for lab2 c is shown below x A program to demonstrate the use of the scanf function x C Programming laboratory 2 x This line allows the compiler to understand both the printf and scanf functions include lt stdio h gt int main void x Declare a variable to store an integer number x int number_entered Output some text to the user printf Ent
195. name of your new file You wish to create a new source file The IDE treats C source files as a special case of the more com Revision 1 3 Computer Programming Using C 121 plicated language C To create a new C source file you should make sure that the C Source File option is selected Type the name for your new file into the File name box as indicated You must ow make sure that your file name ends in c A blank file will appear in the editor ready for you to put some source code in it Copy or cut and paste at least one function into this file You will need to include any header files which the function needs You can now save your new source file Repeat the process until you have the file structure that you decided on If you want to remove a file from your project select the file in the source file tree and press the Delete key This will not actually remove the source file from the folder But it will remove it from the project so it is no longer part of your program You should now have a set of source files which are all part of your program and are all shown in the source file tree on the left hand side of the IDE window Each function in your program should only be in one of these source files Unfortunately you are not yet ready to build your program At the moment there is no way for a function in one file to know about a function in another file To understand this we must look at how
196. namic memory allocation for the structures themselves remember to free any memory that you allocate 15 3 The Limitations of Arrays Only storing pointers in an array rather than the structures themselves is a vast improvement How ever this arrangement still has a number of limitations The largest limitation is that adding or removing a structure to from anywhere in the list other than the top is very difficult It is possible but the process is inefficient Imagine a situation where a list using this technique is needed to store anywhere between a small and large number of structures As the array of pointers is statically allocated if only a small number of its entries are being used this is very wasteful If we make the array of pointers small we must dynamically reallocate it when it is full to prevent overflow This is very inefficient The rest of this lab introduces linked lists which get round all of these problems 15 4 Introducing Linked Lists To begin with consider the example of an array of four student structure pointers that was introduced above Imagine that each of the four pointers in the array each referenced a structure 0x12345678 Family Name Given Name Year of Birth Course Code 0x12345678 students 0 0x23456789 Family Name Given Name Year of Birth Course Code 0x23456789 0x34567890 Family Name 0x45678901 t 0x34567890 Given Name Year of Birth Course Co
197. nction declarations In this context void means nothing You can see from this line that function heads are made up of three parts type of_return value function_name parameter_list We do not need the display welcome to return a value so we specify its return type as void We do not need any extra information for the function to work i e when the function is called there is no need to specify any arguments So we put void in the parentheses after the function name When the main function called the display welcome function it did it like this Revision 1 3 Computer Programming Using C 91 display_welcome You can see from this line that there was no return value to assign to variable and no arguments were specified This matches the function head for display welcome The square function is a bit different The function head looked like this int square int value This function head declares the square function to return a value of type int and to require it to be called with one argument of type int When the argument reaches the function it is given a name value It is then called a parameter Parameters are very like variables they have a type and a name You can declare many parameters for a function in a list separated by commas Each parameter in the list must have its own type Parameters also have the same scope as a local variable declared in that function You can only use the parameter as a variable inside the functi
198. ne n return 0 Let us look at the switch statement in detail It begins with the keyword switch followed by the name of the variable that we wish to switch on in parentheses Like this switch number_entered We then describe a number of cases which are different options for the value of the variable given in the switch part All these cases are enclosed in a set of braces like a compound statement The switch statement looks for the first case clause that matches the value of the variable When it finds it it starts executing from that point onwards Let s take the example where the variable number_entered has the value 4 The switch looks down its list of case clauses until it finds the one that say case 4 it then starts executing at that line so the next thing it executes is the line printf four n The next line says break which tells it to stop executing the code inside the switch statement and to continue after the closing brace You should also notice that there is a special case clause called default This gets executed if none of the other case statements before it match Because the switch statement attempts to match case clauses in order the default clause should always go last 50 Computer Programming Using C Revision 1 3 Syntax switch statements switch variable case clause default_clause The switch statement allows you to make a choice between a number of options Each
199. ne scales e Try some different scales other than a major scale e Try choosing which scale will be played at random e How about representing chords using an array Can you get your program to improvise a chord line to accompany a melody built out of scales e Can you use the value of an array to predefine some pause values This would allow you to predefine certain rhythms Try playing these rhythms on MIDI channel 10 this is the drum chamnel 118 Computer Programming Using C Revision 1 3 6 9 Summary Now that you have finished this laboratory you should understand what arrays are and how they can be used You should be able to declare both single and multidimensional arrays and initialise them with data You should know that strings are character arrays and that all strings in C are null terminated so they end with the null character 0 You should be able to manipulate strings and create them using the scanf and sprintf functions In the graphics option you added to your program to make it much more like a computer game It should now have a target towards which the user throws the object The user should then be given a score for their throw In the music option you should have found that arrays are very useful for defining sections of music by representing numerical relationships You should understand how to use an array to represent a scale You may also have explored how to use arrays for chords and rhyth
200. ng version We can now define a new type as shorthand for struct long_student_type typedef struct long_student_type student_type This new type is easier to use than the old one because we can omit the st ruct keyword when creating variables So student_type student declares a new variable called student of type student_type When using type definitions with structures it is usual to combine the struct definition and the typedef all in one statement Like this typedef struct long_student_type char family_name 40 char given_name 40 int year_of_birth int course_code student_type This defines a structure struct long_student_type and creates a shorthand for it called student_type all in one line As with other type definitions the best place to write this code is in the global scope Syntax Type Definitions typedef old_type_name new_type_name A typedef statement defines a new name for an existing type The new name is an exact replace ment for the old name it can be used interchangeably with the old name i e it is a synonym The old type name is still valid For example typedef double Length Defines a new type called Length which is equivalent to the double type Exercise 11 2 Using typedef with Structures Change the lab11 program to use a typedef for the structure type so that the keyword struct does not need to be used when declaring variables Ensure that the ty
201. nt it puts the result in is decided by the value of the curr_data_value variable The value of the curr_data_value variable is set by the for loop The for loop will stop when it gets to the tenth element in the array data values 9 It will also stop if the done variable is assigned a value other than zero This is controlled by the condition part of the for loop To calculate the mean the array is passed to another function called mean Note how the parameter which receives the array is declared The prototype for the mean function looks like this double mean double values int num_values The array is declared with empty square brackets because we don t need to limit this function to only working with arrays of a certain size In this case the function just needs to know how many values out of the array to use Even if the program always used the whole array we would still need to pass the size Of the array as a parameter to the function There is no way to determine the size of an array in C You must store it in a variable somewhere or you must fix it at the time when you write the program Exercise 6 1 Understanding the Array Program Make sure you understand how the lab6 program works Try stepping through some or all of it if you are unsure If you only want to step through some of it perhaps you only want to step through the mean function then use a breakpoint to interrupt the program when it reaches the part you are
202. nto the same source file twice If the header file only contains pro totypes this is not a problem because you can declare the same prototype as many times as you want as long as the definitions are the same Later in the course you will put more complicated things in header files which can only be seen by the compiler once for each source file it processes Both of these problems can be solved if we make sure that the contents of a header file are seen only once by the compiler for each source file We can do this by using the define ifndef and endif preprocessor directives you met in laboratory 4 Revision 1 3 Computer Programming Using C 125 Let us take the example of a header file called graph_fun h At the top of the header file there should be a line which checks to see whether a label has been defined The label must be unique to the header file To try and ensure that the label is unique the name of the file is often used in some way It is most common to use a label which is made of two underscores _ the name of the file except for the h extension another underscore the letter H and finally another two underscores As with all preprocessor labels it is good programming practice to use only UPPERCASE letters for these labels For example for the header file graph_fun h we would use the label __ RAPH_FUN H We would check whether it is defined using the preprocessor directive ifndef l
203. number of functions for working with memory The normal way to allocate a block of memory is to use the malloc function which is an abbreviation for memory allocation When you are finished with the block of memory your program must hand it back using the free function To demonstrate the use of malloc and free we will look at a very simple program snippet The bit of code we will look at simply allocates some memory we imagine that it uses it and then the memory Revision 1 3 Computer Programming Using C 177 is freed When the memory is allocated we will use the pointer my_array to reference it When the program starts the pointer does not yet have a meaningful value int main void 0x89012345 my_array int my array my_array malloc size free my_array return 0 The call to malloc allocates a block of memory of a specified size The code snippet has the word size where you would specify the size of the block of memory you require We will look at how to specify memory sizes in a moment Imagine that we specified that we wanted room for four integers int main void 0x89012345 0x12345678 my_array int my array my_array malloc size free my_array The diagram shows that we have allocated a block of memory and that the pointer my_array references it Notice that the block of memory has no variable name It is not a variable the only way we have to access this memory is using the my_array pointer
204. o make sure that each number is on a new line in the file The next exercise will use the random_number function from the defined in the music library header file midi_lib h Those doing the music option will already be familiar with this function The function generates an integer random number within the bounds that are specified by the two arguments to the function For example the function call number random_number 1 10 Will assign a random number to the number variable The random number will be anywhere between and including 1 and 10 Function Reference random_number Generates a random number int random_number int lower_range int upper_range The random_number function returns a random number which could be anywhere in the range lower_range to upper range including the values lower_range and upper range For exam ple pitch random_number 60 71 will assign a value to pitch that could be 60 71 or any integer value in between random_number is defined in midi_lib h Exercise 17 3 Writing Multiple Numbers to a File Alter the lab17 so that it fills an array of 40 elements with random numbers and writes all of the numbers to a single file Each number should be on a new line in the file Open the file you have written into to check the write operation worked correctly Adjust the program to write 500 random numbers between 1 and 100 toa file called unsorted txt Keep this file you w
205. o understands C but doesn t understand how your program works The program begins with the line int main void This states that all of the C code between the two braces or curly brackets is part of a function called main Every C program has a main function which is the place where the program starts execut ing At the moment the main function is the only function in this program Later on in the lab you will use or call some other functions that are often used in C In laboratory 5 you will learn to create your own functions The next part of the program lists the variables we are going to use in this function int distance_to_tokyo distance_to_airport int speed_of_plane speed_of_car int time_to_fly time_to_drive time_to_tokyo int average_speed Revision 1 3 Computer Programming Using C 17 Variables are used in programs in much the same way that x y and z for example are used in algebra to represent values The computer needs us to tell it what variables we will be using before we use them To do that we need to tell it what the variable is called and what kind of information it will hold This is called the variable type In C terminology we declare the variable and its type Syntax Variable Declarations type name name e g int an_integer_variable double a_real_variable ae OME sae WereielolSe momias dame weicalollhes Variables are placeholders for values just like in algebr
206. o_tokyo 13 m Go To Reference To distance_to_tokyo lri M Insert Remove Breakpoint ec ok MM Enable Breakpoint IEE AN GlassWizard __ ES Properties Ne 1 Select the option Insert Remove Breakpoint SP You should find that the line in the source code that you clicked on now has a small red dot at the left hand side of the line like this Calculate time taker o time_to_fly distance time_to_drive distanc This indicates that the line in the source code has a breakpoint on it Start the program running in the debugger by selecting Build Start Debug Go SP AAA AAA H clab lab4a lab4a c t Build Tools Window Help amp compile lab4a c Ctrl F7 Clean Debugger Remote Connection Execute lab4a exe Ctrl F5 3 Run to Cursor Ctrl F10 Configurations Profile lables for the calculai yo distance _to_airport 82 Computer Programming Using C Revision 1 3 You should see that the program starts running until it reaches the breakpoint It then stops the pro gram but you have the chance to continue the program from where it is using the step commands or to continue running using the Go option on the Debug menu When the debugger stops on a breakpoint it is exactly as if you had used the step commands to get there just a lot quicker You can remove a breakpoint by clicking on the line of source code with the breakpoint on it using the right
207. ocation which is being used to store the information for that variable For example amp some_variable is directly equivalent to the address of the variable some_variable The dereference operator carries out the opposite operation to the reference operator it takes an address in the form of a pointer and follows it to find the location that it refers to So if some_pointer amp some_variable some_pointer is directly equivalent to some_variable i e the lines some_pointer 20 some_variable Por do the same thing The dereference operator is used when declaring pointer variables as in type xname For example the line int some_pointer Declares a new variable called some_pointer which is a pointer to a variable of type int You might have noticed that a pointer variable is declared using the dereference operator like this int ref_my_integer This is saying I would like to declare a variable with a type such that if you were to dereference it you would get an int If you dereference the ref_my_integer variable you get an integer 12 4 Using Pointers to Pass Parameters by Reference The reason we started looking at pointers was to change the way parameters are passed into functions The next thing you will do is to change the simple program lab12 you met at the beginning of this lab so that the change function can alter the value of the argument variable in the main function This can be d
208. of Birth Course Code students 2 students 3 194 Computer Programming Using C Revision 1 3 An array of structures uses enough memory to be able to store all the data items for each of the struc tures that form the array So an array of 100 structures is 100 times the size of a single structure in memory If the buffer is empty this arrangement is exceedingly wasteful of memory A way to solve this problem is to create an array of pointers and manage the array just like a LIFO buffer use a variable to tell us how much of the array is being used and how much is free The pointers in the used section would all reference structures We would declare an array of pointers like this student_type students 4 All this does is create an array of pointers which to begin with are undefined Undefined students 0 Undefined students 1 Undefined students 2 Undefined students 3 We would record the number of students that the arrays holds in a variable Initially this variable would be set to zero A pointer does not use very much memory so this array is considerably smaller than the array of structures When we want to add a student we allocate a new structure using malloc and save a pointer to it in the array For example student_type new_student new_student malloc sizeof student_type students 0 new_student This sets the first pointer in the array to reference the new stru
209. of linked list which alleviates many of these problems 16 2 The Limitations of a Single Linked List The kind of linked list you have been working with so far has a single pointer in each structure which references the next structure in the list Because there is only one pointer in each structure this is called a single linked list A single linked list is very simple and very efficient In this section you are going to explore some of the difficulties with single linked lists The largest problem with single linked lists is caused by the fact that the references that link each of the structures only go in one direction This means that if you are at a particular point in a linked list it is difficult to find the item that comes before the one you are looking at In this case the current pointer is referencing the third structure in the list How do we find our way to the second structure in the list For example consider the situation in the diagram below First Pointer Current Pointer The only way to do this is to go back to the beginning of the list using the first pointer and to move along the list keeping track of two pointers e a pointer to the item we are considering call this pointer A this pointer starts at the beginning of the list e a pointer to the item before pointer A call this pointer B 204 Computer Programming Using C Revision 1 3 We will set Pointer A to start at
210. ogram When it has terminated open My Documents from your desktop double click on your clab folder and the lab17 folder You should see a file called number or number txt If you double click on this file it will open You should see that the number you entered into the lab17 program is stored in this file as text Just as writing to a file can be done with fprintf reading from a file can be done with fscanf The fscanf function works just like the scanf function except that it takes an extra first argument the handle of the file that it should read from For example the following line of code reads an integer from a file fscanf file_handle d amp int_variable Revision 1 3 Computer Programming Using C 217 Function Reference fscanf Performs a scanf like read from a file WONG ESC 03 bas Pale Jneumolle clague EON Se AE aso e g iSonic ele memecule Weel fem ame weliesteilolle 2 reCer Geese eile Ve e ele variae number_of matches fscanf result_file S1f a_ double variable The fscanf function obtains textual input from the file identified by the ile_handle argument This handle must identify a file previously opened by the fopen fucntion for reading The input is converted according to the format_string argument The format _ string argument specifies placeholders in an identical manner to the scanf function fscanf takes at least two arguments but like scanf
211. ok like this lab1 Microsoft Yisual C lab1 c B File Edit View Insert Project Build Tools Window Help jals ug e j gt nar aj la Il Globals al All global members main z PRL v alx G Workspace lab1 1 project s lab1 files Sq Source Files Header Files Resource Files ia Elo A program to demonstrate simple mathematical operations C Programming laboratory 1 The main function the program starts executing here int main void Declare some variables for the calculations int distance_to_tokyo distance_to_airport int speed_of_plane speed_of_car int time_to_fly tine_to _ drive time_to_tokyo int average_speed Set the values of some of the variables Set distances in kilometres distance_to_tokyo 9720 distance_to_airport 120 Set speeds in kilometres per hour y Ma ClassView speed of plane 1200 y Ln1 Col1 REC COL OVA READ Z The source code for this program is printed below This is the same as the code in the lab1 project x A program to demonstrate simple mathematical operations x C Programming laboratory 1 x x The main function the program starts executing here x int main void x Declare some variables for the calculations int distance_to_tokyo distance_to_airport int speed_of_plane speed_of_car int time_to_fly
212. on 1 3 Computer Programming Using C 181 In the last part of the lab you should have used dynamic memory allocation with an array of structures 182 Computer Programming Using C Revision 1 3 Laboratory 14 Creating Buffers 14 1 Overview This lab uses the C you have learned so far to examine an important real life application the use of buffers Buffers are simply a way of storing information in your program This lab looks at two different type of buffer and shows you the basic principles of using them To begin with this script looks at what buffers are and why they are useful Two sorts of buffer are then introduced which differ in the way in which information is extracted from the buffer At the end of the lab you will see a more sophisticated arrangement for handling buffers which is used a great deal in practice 14 2 Buffers Flexible Storage A buffer is a part of a software system which stores data In this way it acts a bit like a tank There is a path for information to flow in and a path for information to flow out The tank is useful in situations where the rate of information coming in is different to rate at which information travels out A buffer acts as a flexible way to store a small amount of data Unlike in the picture of the tank above buffers usually store information is some kind of order This lab is going to examine two types of buffer which differ in the way information is taken out of the buffer
213. on body When a function is called there must be an argument for each parameter in the function head The values of the arguments specified in a function call are copied into the parameters before the execution point enters the function body The values are copied in order i e each argument is matched with a parameter in order When the square function was called it looked like this squared_number square number_entered Before the execution point represented by the yellow arrow in the debugger moves into the square function the value of the number_entered variable is copied into the value parameter specified in the square function head squared_value square number entered Argument value copied to parameter int square number_entered When the square function has finished everything it needs to do it uses the return statement speci fying a value to return The type of this value must match the return type specified in the function head square uses the return statement to return the value of an integer variable like this return squared_value The value of the squared_value variable is returned to main and assigned to the squared_number variable squared_value square number _entered Argument value copied to parameter int square number_entered int squared value squared_value value value return value Return value copied back into variable When a function defines
214. on the system the function will return the NULL pointer The malloc function is defined in stdlib h Revision 1 3 Computer Programming Using C 179 Syntax The sizeof Operator sizeof type The sizeof operator calculates the amount of memory a type requires for storage For example the following sizeof int calculates how much size is required by one integer variable sizeof evaluates to a number so it may be combined with mathematic operations such as multiplication For example 1024 x sizeof char The most common use for the sizeof operator is when using the malloc memory allocation func tion Function Reference free Memory Deallocation free pointer The free function deallocates memory that was previously allocated using the malloc function The ree function takes one argument a pointer to the block of memory to be deallocated e The free function should always be used to deallocate memory as soon as it is no longer required e You should never attempt to free a block of memory twice or to free statically allocated mem ory such as arrays e Once a block of memory referenced by a pointer is deallocated the pointer should not be used again unless it is assigned a new value The free function is defined in stdlib h Exercise 13 4 Arrays and Memory Allocation The lab6 program allowed the user to enter data which the program placed in an array Two sta tistical
215. one by changing what we pass into the change function Instead of passing the value of the variable j from the main function we could pass a reference to j using the reference operator amp The change function should then be adjusted to accept and use a pointer to an integer instead of an integer This technique of passing a pointer rather than a value to a function is called passing by reference Revision 1 3 Computer Programming Using C 169 Exercise 12 4 Changing the lab12 Program to Pass by Reference Change the lab12 program to pass the parameter into the change function by reference rather than by value You will have to change e The way in which the function is called You will have to use the reference operator to create pointer e The parameter declaration part of the change function head At the moment the change function accepts a single integer parameter You should change this so that it accepts a pointer to an integer instead e The assignment statement inside the change function to use the dereference operator By using the dereference operator you will affect the value of the j variable in the main function Try building and executing your program You should find that the change function is now able to affect the value of 3 You may have noticed that you have been using the reference operator amp since laboratory 2 in scanf lines like this scanf Sd my_integer This means th
216. opera tions You should know that to begin operating with a file you must open it with the fopen function e when you have finished using the file you should close it with the fclose function e when operating on the file you use an identifier that you obtained from the fopen function called a file handle e you can write to the file using the fprintf function which is very similar to printf e you can read from the file using the scanf function which is very similar to scanf You should have used these concepts to add load and save functionality to the program that you have been working on as part of your option This gives you the ability to save drawings as a file in the case of the graphics option or musical sequences as a file in the case of the music option Laboratory 18 Sorting Searching and Recursion 18 1 Overview This laboratory takes a very brief look at two activities that are often carried out by software programs e sorting where a collection of data is sorted according to some criteria e searching where the presence and position of some item in a collection of data must be determined Both of are very complicated topics in their own right You will only write one program for each of these topics Searching data often uses a technique called recursion A function is recursive if it calls itself This can cause the computer to execute many times just like a loop This lab introduces recursion with a few
217. ort algorithm both for simple arrays of numbers and for more complex situations like strings and linked lists Whilst doing this you will have used the strcmp and st rcmpi string comparison functions In the second part of the lab you learnt about recursion which is a way of looping parts of your program by creating a function which calls itself You should have used this technique to calculate a factorial and to perform a binary search on a sorted array of integers Appendix A Summer Term Laboratory Outline A 1 Overview You have four laboratories in the summer term labs 19 20 21 and 22 Laboratory 22 is set aside for you to demonstrate the software you have developed as part of your second assignment Labs 19 to 21 are free for you to use to work on your assignment You may choose how you want to use these labs however it is suggested that you spend e lab 19 working on your analysis specification and design e lab 20 working on you implementation e lab21 testing your implementation and making any changes as necessary During each of these labs the demonstrators will be available to help and advise you 226 Computer Programming Using C Revision 1 3 Appendix B Suggested Further Reading B 1 Tutorial Material 1 Peter Aitken and Bradley L Jones Teach Yourself C in 21 Days SAMS 2002 2 Paul Davies The Indispensable Guide to C with Engineering Applications Addison Wesley 1995 3 Andy M Tyrrel Stephen L
218. ou might find that an initial velocity of 60ms is suitable for both zx and y directions The code you produce should work whatever horizontal location the user chooses for the stick person You should ask the user for the initial velocity of the object The same initial velocity should be used for both vertical and horizontal components Hint If you really get stuck have a look at the source code in the graphics2 project It should help you If you still do not understand how to do this ask one of the demonstrators for help Exercise 3 7 Allowing the Stick Person to Move Use a get ch function call to wait for the user to press the Enter key before drawing the path of the object This should happen after the stick person has appeared in the graphics window you may need to look back at the script for laboratory 2 to find the key value for Enter Remove the option at the beginning of the program for the user to choose the horizontal location of the stick person Let the user move the stick person before they hit Enter using the left and right arrow keys To make the stick person appear to move you should draw over the top of the stick person with another stick person made up of black lines This will erase the stick person from the screen You can then redraw the stick person in a new position using coloured lines Exercise 3 8 Giving the User Three Goes The program you have now should allow t
219. ou should have learnt about and be able to use e if statements e switch statements You should be able to form relational expressions including quite complex containing with logical op erators You should understand switch statements and the way in which the flow of execution passes through them including the reason for break statements You should also be able to obtain input from the user of your program You should know how to use e scanf to get a complete line of input from the user at one time until the user presses Enter e getch to obtain a single key press In the music and graphics options you should have used these functions to provide various options to the user of your program You should have used conditional statements to process the options and to make sure that none of the input is invalid 56 Computer Programming Using C Revision 1 3 Laboratory 3 Repetition and Iteration do while and for 3 1 Overview This laboratory will introduce you to three ways of repeating parts of your program e the while loop repeats a part of your program whilst and providing a condition is true e the do while loop also repeats a part of your program whilst a condition is true but it will always execute that part of your program at least once e the for loop is a convenient way to repeat a part of your program with a built in counter You should learn how to use these repetition structures and which is
220. ou should know how each type of linked list is constructed and how they can be used You should also understand how to write programs which use linked lists Laboratory 17 File Handling 17 1 Overview Up to this point in the course you have used functions from the standard C library to display information on the screen and receive information from the user This laboratory will introduce you to a set of very similar functions which allow you to both write and read information to from files stored on the computer or a network drive In the final part of the lab you will use this to store information from the program you have been working as part of you graphics or music option 17 2 Getting Access to Files Since very nearly the beginning of this course you have been using the printf function for output to the screen and the scanf function for input from the keyboard This lab will use very similar functions fprintf and fscanf to output and input to from a file Before you can either read or write to from a file you have to request access to the file When you do this the file you have requested is usually locked meaning that only your program can access the file at that time This is called opening the file When you are finished with the file you must close it again When you open a file you are given a pointer which acts a shorthand for the file you are talking about This pointer is called a file handle You get a different file handle
221. ow of your program is logically wrong Only errors will stop the compiler and linker from producing an executable Warnings will not stop it but you should still pay a great deal of attention to them Errors and warnings appear in the output window like this This is just an example You shouldn t be seeing anything like this at the moment bis Configuration labl Win32 Debuy _ _____ Compiling labl c E h clabNlabislabl c 12 error C2065 in undeclared identifier h sclabrabirlabl c 12 error C2146 syntax error missing before identifier dist h clabNlabisNlabl c 12 error C2065 distance_to_tokyo undeclared identifier gt Ls 1 a l al o m h mon mm de mnm mnn d I a sece lt m AS we dee AS Build Debug 4 Find in Files 1 Find in Files 2 Each line in this output is an error Looking at the first line the texth 1clabllab111ab1 cis the name of the file the compiler was working on 12 means that the error was on line 12 error C2065 is the the error number which you can usually ignore All the remaining text is the error message If you cannot understand an error message ask the demonstrators for help We have now compiled our program There are two ways in which we can run it e find the executable file and double click on it to run it e ask the IDE to run it for us The executable file is in a subfolder of the project
222. own the left hand side of your source code a line at a time The debugger will skip lines that it cannot execute such as comments and variable declarations When you instructed the IDE to begin debugging it changed the layout of the main window to contain the watch window Ll Context main X distance_to_airpc 120 distance_to_tokyc 9720 speed_of_car 100 Locate this A This shows you what the contents of variables are at the current point in the program As you step through the program you should be able to see the values change in this window The Auto tab inside the watch window the one that is displayed by default shows you the variables that have changed most recently Sometimes a variable that you want to see the value of is not on this list By clicking on the Locals tab the watch window will show a list of all variables that are local to the current function the main function in this case In the case of the current program the Locals tab will show a list of all variables and their values gF When you reach the last line of the program do not continue to step The debugger will start to try and execute code that is not part of your program which can get very confusing Choose the Go option from the Debug menu to allow the program to terminate Exercise 1 2 Using the Debugger Use the debugger to step through the program Check the watch window after each time you step an
223. pe definition is in the global scope of your program i e outside of any function 156 Computer Programming Using C Revision 1 3 Exercise 11 3 Using Your New Type Name Create a function which displays all of the details about a student Each piece of information should be shown on a separate line Alter the program to use the function to display the contents of the structure in place of the final print f statement The function might have a prototype like this void display_student student_type student 11 4 Using Arrays of Structures At the beginning of this lab the analogy was drawn between a structure and a card with details written on it Usually there are many cards all of the same type kept together in a filing cabinet of some kind So far we have only used one card In this section we will use multiple cards by creating an array of structures An array of structures is easy to create by using the type that your have defined An array of five student records would be declared like this student_type students 5 You can now access individual structures in the array by specifying their index For example students 2 year_of_birth 1986 Exercise 11 4 Using an Array of Structures Edit the lab11 program so that the user is first asked how many students they wish to enter details for This could be a number anywhere between 1 and 10 If the user enters 0 the program should end Ask the u
224. pitch The pitch of the note as an integer value in the range 0 to 127 Middle C has the value 60 e channel The MIDI channel you wish to use to play the note as an integer number There are 16 MIDI channels numbered 1 to 16 each one can be set up to use a different instrument and notes can be playing on all channels at once e velocity The velocity related to volume of the note to be played as an integer value This argument can range from 127 loudest to 0 silent Setting the velocity of a note to zero is used to turn the note off So for example to play middle C on channel 1 at moderate volume you could write machi note 60 1 6 5 which would turn the note on To turn the note off you would write mich more 60 i 015 A note that is not turned off will continue to play forever possibly even after your program has ended midi_note is defined inmidi 1ib h If we turned the note off again straight away it would play for such a short time that you would not hear it To make sure you can hear it we make the computer wait using the pause function pause 1000 You tell the pause function how long to wait for in milliseconds and it does not allow your program to continue until that time has elapsed The pause therefore controls how long the note is played for its duration In this case the note will play for one second 1000ms 1 second Revision 1 3 Computer Programming Using C 35 Function Reference pau
225. pite the buffer being totally empty how many more data items can we add to the queue It is likely that we cannot add more than one data item without the buffer overflowing The way to solve this problem is to imagine the array as if the top element buffer 7 were joined to the bottom element buffer 0 to form a circle We may then continue adding data items to the queue This is called a circular buffer To continue the example from above once we have added seven items to the buffer and removed them suppose we add another two data items 47 and 64 This is shown in the diagram below ffer 7 7 buffer_head 1 buffer_foot ffer 4 ffer 3 ffer 2 ffer 0 Notice that the buf fer foot variable has a lower value than the buf fer _head variable This is a sign that we are treating the buffer as circular and that the queue data has wrapped round from one end of the array to the other Exercise 14 4 Making the FIFO Example Circular Change the lab14 program so that queue is handled as a circular buffer You will need to be careful how you detect and trap the buffer overflow and underflow conditions If you do not understand how to do this ask one of the demonstrators for help 192 Computer Programming Using C Revision 1 3 14 7 Summary Now that you have finished this lab you should know what a buffer is and how one might be con structed using an array You should know about two important type
226. place the circle in the right place for you to draw your stick person Add four line function calls to draw the lines to make up the stick person s body arms and legs This may take a lot of experimentation It helps if you draw it out on paper first and try and work out what coordinates you will need Remember that the origin of the z and y axes is in the top left of the window Plot the lines using the x position and y position variables For example line x_ position y_position 10 x_position y position 50 This means that changing the x_ position and y_position variables moves the location of the whole stick person not just the circle Ask the demonstrators for help if don t know how to complete this exercise 1 8 Music Option You should only begin this section if you have chosen to do the music option i e if you are a Music Technology student or if you have chosen to do the graphics option but have already completed that section As an example of how to use C we are going to investigate how to get the computer to make sounds Although this is not strictly part of the C language the principles are important for all C programming We will be using the computer s MIDI facilities to produce sound MIDI stands for Musical Instrument Digital Interface and is a way of connecting electronic musical devices together such as keyboards synthesisers and computers Elsewhere in your Music Technology course you will learn
227. ple lab1 Then click the Open button to open the workspace Summary If you have read this section in full then you should have learned 10 Computer Programming Using C Revision 1 3 e how to map you N drive e how to create a folder for your work which are things you should only have to do once You should also have learned how to carry out tasks you will need to do in every laboratory e how to copy a project e how to open the IDE e how to open a project in the IDE All these tasks will be an essential part of the first lab Part I Autumn Term Laboratories Laboratory 1 A Simple C Program in Microsoft Visual Studio 1 1 Overview In this first laboratory you will be introduced to the Microsoft Visual Studio integrated development environment IDE You will be using this software to write and test C programs This lab will also introduce the following concepts e the structure of a simple C program e variables their names and types e how to do simple mathematics in C e how to call functions e how to use the printf function You should understand all of these concepts by the end of the lab You will also have been introduced to either the graphics or the music facilities 1 2 Setting Up Before you begin this lab you should have read the Introduction and Before You Begin sections Before we can begin the lab it is essential that you have carried out the first two tasks
228. ple whole tone scales with drone tones in the background You should also have learned how to detect when the user has pressed a key and used this to allow the user to choose when your program should stop 72 Computer Programming Using C Revision 1 3 Laboratory 4 The C Preprocessor and Useful Debugging Techniques 4 1 Overview This laboratory covers a number of different topics that are useful to know about when constructing and particularly troubleshooting debugging your C programs We will look at e a part of the compiler called the preprocessor which deals with all of the lines in your code that begin with a hash or sharp symbol e how to use preprocessor commands to stop parts of your program from compiling e how to use conditional compilation for debugging e setting breakpoints and using them for debugging your program e finding the executable file that corresponds to your program and running it without the IDE Some of the tasks you do will be different depending on whether you are following the graphics or music option but there are no special sections for the different options in this laboratory 4 2 Stages of Compilation When you build a project the output window shows messages generated by the compiler If everything goes well the output window looks like this oo Configuration labi Win32 Debug Compiling labl c Linking labl exe 0 error s
229. program has been tested is often called the test coverage Your testing and verification report should e describe your testing strategy to show that your program works correctly under all conditions e explain why you think you strategy is sufficiently comprehensive e include all test input data and test results and comment on your test coverage e detail any modifications you made following test failure and show the results of re testing 8 5 8 User Manual You can imagine that most of your software report is written for someone who understands software development in C and wants to understand your program The user manual on the other hand is written for the user that you identified in your analysis It may be that this user is not technically literate That way that your user manual is written should reflect the type of person you think will be using your program Your user manual should include e installation instructions this may just be copying the executable file for your program e user and system requirements you should say what type of computer is necessary to run the program and what kind of expertise you are expecting on behalf of the user e full usage instructions for all your programs features ideally with examples e you might also like to include answers to frequently asked questions FAQs 8 6 Summary Now that you have finished this laboratory you should have a good idea of what needs to be in a softwa
230. ptions that you are interested in There is also an special case for all number of case other options labelled default The lab2a proj and execute it The source code x ect demonstrates the switch statement in a very simple way Copy the project build for lab2a c is shown below A program to demonstrate the use of the switch statement x C Programming laboratory 2 x include lt stdio h gt int main void int number_entered Outpu t some text to the user printf Enter an integer number between 1 and 9 Wait for the user to enter a number and hit enter x Store the number in the number_entered variable scanf d number_entered Display the number that the user entered x But d isplay it as English text x printf The number you entered was x This switch statement decides between lots of options x switch case 1 prin brea case 2 number_entered t one n Ky prin t two n break case 3 printf three n break case 4 printf four n break case 5 printf five n break case 6 printf six n Revision 1 3 Revision 1 3 Computer Programming Using C 49 break case 7 printf sevenin break Case 8 printf eightin break case 9 printf nine n break default printf not between one and ni
231. r new header file you should make sure that the C C Header File option is selected Type the name for your new file into the File name box as indicated You should make sure that your file name ends in h Exercise 7 3 Creating Header Files You should now create a header file for each one of your source files which contains functions that are used by another file For example if the file music1 c contains functions that are called only by other functions inside the music1 c file there is no need to create a header file for it Use appropriate include lines to allow you to remove function prototypes from your source files Your program should still build and execute correctly 7 4 Protecting Your Header Files You have just created header files which allow you to encapsulate a set of functions in a source file in a way that makes them easy to use in other source files Sometimes header files will have include di rectives in them which include other header files These header files may also have include directives and so on The process can become very complicated In these situations two problems can occur e a circular reference can occur This is where one header file includes another header file which includes the original header file The compiler would then travel round this loop forever actually it would run out of memory and crash which is probably worse e a header file can be included i
232. r variables in the new item e set the next pointer of the new item to NULL e set the first pointer to reference the new item The result of this is shown in the diagram below 0x45678901 Family Name Jones qe 0x45678901 students Given Name rancis Year of Birth 1974 Course Code 636 Next Pointer NULL The steps for adding the next item to the list are slightly different After allocating the new structure and setting up the member variables to store data we must set the next pointer The situation at this point is shown in the diagram below 0x34567890 Family Name Bloggs Given Name Fred Year of Birth 1982 Course Code 606 Next Pointer Undefined 0x45678901 Family Name Jones 0x45678901 student Given Name Francis x iS Year of Birth 1974 Course Code 636 Next Pointer NULL We wish to insert the new structure before the structure that is already in the list To do this we copy the value of the first pointer into the next pointer of the new structure This makes sure that the new structure references the same thing that the first pointer does Revision 1 3 Computer Programming Using C 199 0x34567890 0x45678901 0x45678901 students Finally we make sure that the first pointer references the new structure and the list is complete again 0x34567890 0x34567890 students 0x45678901 To summarise the steps that we followed this time were e alloc
233. re design and how you might go about writing one yourself You should also know that the reference section of this lab will be useful to you when you come to write your own software reports 144 Computer Programming Using C Revision 1 3 Laboratory 9 Assignment Work 9 1 Overview This laboratory has been left open for you to work on any parts of previous labs that you have not finished yet or to work on your assignment with the help of the demonstrators 146 Computer Programming Using C Revision 1 3 Part Il Spring Term Laboratories Laboratory 10 Assignment Demonstration 10 1 Overview In this laboratory you will be asked to demonstrate the software that you have been developing as part of your assignment to the demonstrators You will not be able to ask for assistance in this session 150 Computer Programming Using C Revision 1 3 Laboratory 11 Structures and Defining New Types 11 1 Overview In laboratory 6 you saw how arrays could be used to collect information together in a useful way This lab introduces structures which are another way of collecting information together In an array all the entries must be of the same type The information stored in a structure may be of many different types Structures allow you to write more compact programs and make them much easier to design and understand This laboratory will also introduce you to the typedef statement which allows you to define your own type
234. re have up to 16 different instruments e g violin piano synth etc each on its own MIDI channel The channels are numbered 1 to 16 The musical pitch is specified by a number Each semi tone each note on a piano like keyboard has its own number Middle C for example has the number 60 The C immediately above middle C has the number 61 the D above that has the number 62 and so on There are 12 semitones in an octave so the octave below middle C has the number 48 60 12 48 and the octave above has the number 72 MIDI 34 Computer Programming Using C Revision 1 3 can produce notes in a range a few octaves wider than a standard piano the lowest note number is 0 the highest is 127 The other thing you must specify when turning on a note is the velocity This is equivalent to how hard or fast hence the term velocity the key on a piano or synthesiser would have been pressed to produce a note of this volume Velocity is therefore a specification of the loudness or power in a note It ranges from 127 the loudest down to 0 slient In fact MIDI uses a velocity of 0 to turn a note off You will see this in a moment where we instruct the computer to turn the note off Function Reference midi_note Starts or stops a MIDI note playing midi_note pitch channel velocity The midi_note function sends a signal to the computer s MIDI device allowing you to turn notes on and off It has three arguments e
235. reated specially This is called an escape sequence If you want to specify a backslash in C you have to type the escape sequence for a backslash which is two backslashes Revision 1 3 Computer Programming Using C 25 Exercise 1 3 Using the double Variable Type You should have noticed that because the program uses integer variable types it produces an answer of 9 hours when the correct answer is 9 2 hours To get the correct answer you should use the double variable type e Change the variable declarations so that the type of all variables is now double rather than int e Change the format specifier in the print f function call to be 1f rather than d You should now be able to rebuild your program and execute it Exercise 1 4 Calculating the Proportion of Time Spent in the Air Your program should now display the fact that it takes 9 2 hours to get to Tokyo You are going to add some code of your own to display the percentage of the total time which is spent on the aeroplane It should also display the percentage of time spent in the car obviously the sum of the two should be 100 Your program should display something like x percent of time is spent in the aeroplane x percent of time is spent in the car with the xs replaced by the results of the calculations you have added Some hints e you will need some more variables Choose their names carefully e you will need to add some calculations of
236. red Output some text to the user x printf Enter an integer number x Wait for the user to enter a number and hit enter x x Store the number in the number_entered variable scanf d number_entered Display all the numbers from the one entered x x up to and including the number 10 x while number_entered lt 10 printf d n number_entered number_entered number_entered 1 return 0 You should find that this program asks you for a number and then displays all the numbers from the one you entered up to and including the number ten If you enter a number greater than ten it doesn t display anything You will notice that in the example the whi 1e clause has a compound statement underneath rather than a single statement This allows us to repeat more than one statement Try stepping through the example program Do you see how the execution point jumps backwards inside the compound statement underneath the while clause Make sure you understand how the example works before continuing If you have any problems ask one of the demonstrators Syntax The while Loop while relational_expression statement The while structure allows you to repeat a single statement many times The while statement will execute for as long as the relational_expression is true If you want to repeat or loop many statements rather than just one statement including the semicolon should b
237. rent things take up The sizeof operator looks like a function call but is in fact built in to the C language To use sizeof you specify the type name for a variable in brackets after the keyword sizeof For example if you want to know the size of an integer you would write sizeof int The size of four integers would be sizeof int gt 4 Therefore to allocate space for four integers using malloc you would write my_array malloc sizeof int 4 The code snippet we have been looking at is in the lab13a project Copy this project and open it in the IDE Exercise 13 3 Investigating Memory Allocation Have a look through the source code for the lab13a project Do you understand what it is doing Once you have tried executing it try stepping through it and watching the variables If you cannot understand what is happening ask one of the demonstrators to explain it to you Function Reference malloc Memory Allocation ponte smallkoe size ys e g some_pointer malloc sizeof int real_array malloc sizeof double 20 string malloc sizeof char 256 The malloc function allocates a block of memory of the requested size and returns a pointer to the memory Once the memory is not longer required it must be deallocated using the free function Should the malloc function be unable to grant the request for memory for example if there is insufficient remaining free memory
238. ress c to clear your drawing Press q to quit Press any key to start drawing The program should then wait for a key press Once the user has pressed any key the graphics window should be displayed To ensure that the window fits comfortably onto most people s screens the graphics window should have a drawing area of 640 by 480 pixels To allow these numbers to be changed easily they should be defined as symbols Symbol Name Value WINDOW_SIZE_X 640 WINDOW_SIZE_Y 480 Once the graphics screen is displayed the drawing may begin Drawing should begin at the centre of the screen i e at the location WINDOW_SIZE_X 2 WINDOW_SIZE_Y 2 When the user presses a key it should be handled as follows the up arrow key should cause a line to be drawn from the current location upwards for a small amount the right arrow key should cause a line to be drawn from the current location right for a small amount the down arrow key should cause a line to be drawn from the current location downwards for a small amount the left arrow key should cause a line to be drawn from the current location left for a small amount the c key should cause the drawing to be cleared and the drawing location reset to the middle of the screen the q key should cause the program to exit All key presses should be case insensitive Once a line has been drawn the curr
239. rive Syntax Mathematical Operators ue os eh CS The example source code lab1 c contains a few of the mathematical operators that C supports The standard ones are e addition e subtraction e multiplication e division When there are multiple operators on a line some basic rules are followed operators are looked at by the C compiler from right to left and a special order is followed This order is known as operator precedence and means that multiply and divide are considered more important than add and subtract For example 6 4 2 gives a result of 8 This is the same as the way that they are used in mathematics Quite often you want to clarify what you mean you can use parentheses brackets and for this purpose For example G r a AA a2 gives a result of 5 Revision 1 3 Computer Programming Using C 19 The last line of the main function before the closing brace is return 0 This stops the computer from executing any more of the main function and because the main function was the first function to run there is nothing to run afterwards So the program ends The value 0 is called a return value We will see a little more about this later in this lab and a lot more about it when you come to write your own functions other than main Exercise 1 1 Understanding lab1 c Before we continue you should make sure that you understand what is happen
240. rogram _change function to set up two different voices on two different MIDI channels Add some simple chords to your tune just a few will do which should play at the same time as the melody but on a different channel If you don t know how to do this ask the demonstrators for help 1 9 Summary Now you have completed this lab you should have some understanding of the basic structure of a C program You should also e understand how to declare variables and choose their type 38 Computer Programming Using C Revision 1 3 e be able to carry out some simple mathematics in C e understand what a function call is and be able to call some simple functions such as printf If you chose the graphics option then you should understand the basic structure of a graphics program including how to display and close the graphics window You should also be able to draw circles and lines in many colours If you chose the music option you should be able to instruct the computer to play notes of any valid pitch and on any instrument You should have learned that with MIDI notes need turning on and off and that the time between the two is the note s duration You should also have learned how to play chords Laboratory 2 Conditional Statements The if and switch Statements 2 1 Overview This laboratory will introduce you to the if and switch statements Both allow your program to make decisions You will learn how to form relatio
241. rom the menu Revision 1 3 Computer Programming Using C 7 qgrvucrs yJ Ha E labi Open Browse with Paint Shop Pro 8 Explore Search Make Available Offline Scan with Sophos Anti virus o DP Send To gt a a co Cut Create Shortcut Delete G labs Rename I Properties e You can close the projects folder windows now if you want to Double click the My Documents icon on the desktop When a window appears double click the clab folder that you created to view its contents Click on the Edit menu and select Paste File Edit View Favorites Tools Undo Delete Ctrl 2 Gut Ctrl g Gopy Gtr E Ctrl V Paste Shortcut Gopy To Folder Bl Moye To Folder Ther Select All ctrl 4 Invert Selection See also e The folder containing the project will have been copied into your clab folder Opening the Integrated Development Environment IDE You will do all your programming using Microsoft Visual Studio which is an integrated development environment or IDE You will need to open the IDE every time you want to work on a C program e Click on the Start button on the task bar and follow the menus Programs Programming Microsoft Visual Studio Microsoft Visual C and then select the icon for Microsoft Visual C FS Micr t Visual C gt Microsoft Visual C gt 8 Computer Programming
242. ry location in the block An array that is declared as 174 Computer Programming Using C Revision 1 3 int my_array 4 Can be drawn diagrammatically as a 0x89012345 my_array 0x12345678 It ay my_array 0 0x1234567C MEN my array 1 0x12345680 A my array 2 0x12345684 A my array 3 The variable name my array is actually a pointer this is shown on the left hand side of the diagram This pointer references the first location of a block of four integer sized memory locations The block of memory locations is shown on the right hand side of the diagram When you use the square brackets after an array name it is very similar to using the dereference operator x In fact writing my_array 0 5 is exactly the same as writing xmy_array 5 Accessing any element other than the first element in an array requires placing a non zero number in the square brackets The pointer equivalent to this is to add a number to the pointer Like this my_array 3 20 Which is exactly the same as writing my_array 3 20 Using mathematical operations such as addition on pointers is called pointer arithmetic and must be used carefully Pointer arithmetic changes what the pointer is referencing There is nothing in C to stop you changing a pointer so that it does not reference a valid memory location This mistake often called a floating pointer is very difficult to spot and generally causes your program to crash complete
243. s like int double etc This is most useful when used in combination with structures The graphics and music options each show you one way in which structures can be put to good use 11 2 Introducing Structures Imagine that we want to write a program to store details about students attending a course at a univer sity Let us say that we want to be able to store the following pieces of information about the student e their family name or surname e their given name or first name e the year in which they were born e the code of the course they are on Before computers were used to store this kind of information it would be common to put each of these details on a card The card could then be filed with other cards which have the details of other students Family Name Given Name Year of Birth Course Code A card is useful because it keeps the various pieces of information about the student all in one place 152 Computer Programming Using C Revision 1 3 In C we have used arrays to keep pieces of information together like distances or positions or notes ina musical scale In an array all the items must have the same type This can be very limiting The details we want to store about each student are not naturally all the same type e the family and given names are character strings e the year in which they were born is an integer e the course code is a three digit integer There are two strings and two inte
244. s beginning to get quite sophisticated The user now has control over the hor izontal position of the stick person and the launch angle of the projectile You are now going to add a target for them to throw the object at The target should be at ground level and have numbers on it identifying the score associated with a particular area It could look something a bit like this F of ht E amp TA 10 20 30 20 10 How many areas there are and what the scores are for each area is entirely up to you The best way to produce the target is using a loop Each iteration of the loop should produce one of the small vertical lines which separate the scores You could store the associated scores in array a bit like this int scores 5 10 20 30 20 10 The code that you write to produce the target should have a structure a bit like this int line char label 3 for line 0 line lt 5 line x Calculate position of line based on the value of the line variable Draw the line in the right place x x Calculate position of label based on the value of the line variable x 116 Computer Programming Using C Revision 1 3 x Create a string with the label in it x sprintf label Sd scores line x Use outtextxy to display the text outtextxy x y label Draw the last line here x This is obviously just a skeleton you will need to fill in the missing sections with code of your own
245. s copied into a parameter which acts like a variable inside the function This is called passing by value You will then be introduced to a special kind of variable called pointers which rather than store a value of their own reference another variable A pointer allows the program to find and modify another variable In the next part of this lab you will use pointers when calling functions to allow them to modify the variables that have been passed as arguments This is called passing by reference In the final part of the lab you will use pointers with structures to improve the way in which your programs from lab 11 are written 12 2 More About Function Parameter Passing This laboratory will introduce you to a useful and very powerful technique for working with variables Before you can go on to this we will take some time to look at the way in which variables work when functions are called We will use very simple pieces of C code to understand important concepts The source code below is from the lab12 project Copy the project and open it in the IDE Don t execute the program yet void change int i printf The number is now d n i i 20 printf The number is now d n i int main void int J j 5 printf The number is d n j 162 Computer Programming Using C Revision 1 3 change Jj printf The number is now d n 3 return 0 You will see that there are two functions in
246. s details of things you will need to do in order to prepare for writing and compiling C programs This has been put in a separate section to make it easier to refer to as you work your way through the lab scripts The first two tasks must be completed before you can start with anything else but they should only ever need doing once mapping your N Drive e creating a folder called clab for your work The next three tasks are things you will need to do quite a lot The instructions are in this section rather in the main lab scripts so that you can refer to them copying an existing project from the N drive e opening the integrated development environment IDE e opening an existing project in the IDE The lab scripts will tell you when you need to copy a project and which project you should copy Mapping Your N Drive Configuring or mapping a drive provides a network connection to one of the Department of Electronics servers and gives you access to all of the material needed for this course You should only need to complete this once e Using the right hand mouse button click on the My Computer icon on the desktop My Computer e You should get a menu which looks like the one shown below 4 Computer Programming Using C Revision 1 3 Open Browse with Paint Shop Pro 8 Explore Search Scan with Sophos Anti Virus Map Network Drive Disconnect Network Drive Create Shortcut Rename Proper
247. s of buffer stacks LIFOs and queues FIFOs You should understand two problems that can arise when using buffers overflow when the buffer is full and underflow when the buffer is empty In the case of queues you should also understand how to manage these as circular buffers making best use of the storage space available Laboratory 15 Lists and Queues 1 15 1 Overview This laboratory starts by looking at arrays of pointers as a way storing information This approach gives a lot of flexibility without taking up too much memory The next section of the lab begins by examining some of the problems with storing large amounts of data in an array The solution to this is something called a linked list This is a useful way to store large amounts of data very efficiently This course will introduce you to two kinds of linked list the first is presented in this lab you will meet the second kind in lab 16 15 2 Storing Arrays of Pointers Lab 14 introduced buffers which stored integer data items in an array If you wanted to store more complicated information student details for example you could create an array of structures For example say that we create an array of four student_type structures of the kind that we used in lab 11 student_type students 4 In memory this array looks something like this Family Name Given Name students 0 Year of Birth Course Code Family Name Given Name students 1 Year
248. s the st dio library to clear out flush whatever it has in its input buffer The name stdin is the name of input buffer which receives input from the keyboard stdin is short for standard input and the variable is defined in stdio h There are other buffers that are used in this way In general these buffer variables are called streams Revision 1 3 Computer Programming Using C 89 Function Reference lush Flushes a stream fflush stream e g SI STELLA A Clears a buffer identified by stream that is being used for input or output The most common usage of fflush is to make sure that the input buffer is emptied after a scanf call which had unmatched placeholders In this case the return value of scanf would be tested to determine how many placeholders were matched If scanf did not manage to match all of its placeholders than there will still be characters left in the input buffer In this situation fflush should be called to remove unmatched input from the buffer There are three predefined streams which may be used with f flush e stdin the standard input stream usually the keyboard e stdout the standard output stream usually the screen e stderr the standard output stream especially for error messages this is also usually the screen fflush stdin stdout and stderr are defined in stdio h The next line in the main function after the end of the while loop is another function call resu
249. se Waits for a specified amount of time pause duration The pause function causes the computer to wait before continuing The amount of time the com puter waits for is determined by the durat ion argument which is a integer number and specifies the amount of time the computer should wait for in one thousandths of a second milliseconds For example pause 500 will cause the computer to wait for half a second 500 milliseconds before continuing pause is defined in midi_lib h After the program has waited for 1 second the note is turned off midi_note pitch channel 0 Notice that the correct pitch and channel must be specified so that the computer knows which note to turn off Exercise 1 8 Experimenting with MIDI Experiment with changing the values relating to the note that is played in the musicl example Try altering e the pitch e the velocity e the duration the pause function argument After you have made a change remember to rebuild the program and execute it to see the results When you are happy with creating different notes and durations try to get the computer to play a set of notes one after the other Build up a set of notes to form a tune You can use the Copy and Paste commands on the Edit menu in the IDE to copy sections of code multiple times This should save you having to type the same sections again and again If you don t know how to do this ask t
250. ser for the details of as many students as they specified The student details should be stored in structures in an array When the user has entered all of the details the program should display all of the information stored in the array This should be achieved by calling your display_student function repeatedly in a loop If you do not know how to attempt this ask one of the demonstrators for help 11 5 Graphics Option A structure can be used to store information about a graphical object such as a line or a shape Vector graphics editing programs manipulate information about graphical objects in this way In this lab you will store the information for a set of lines in a structure A line can be fully defined by e its start coordinate x y e its end coordinate x y e its colour an integer value Revision 1 3 Computer Programming Using C 157 This information could be stored in a structure like the following typedef struct long_line_type int start_x start_y int end_x end_y int colour line type The project graphics3 contains the skeleton for the program you are about to write Copy the project g and open it in the IDE Exercise 11 5 Using Structures for Graphics Write a program which prompts the user for the coordinates and colours of a number of lines You might like the user to be able to state how many lines they want to use although you will probably have to impose a maximum
251. sing C Revision 1 3 Exercise 15 5 Adding Remove Functionality Implement the 1ist_remove function so that it removes the first item from the list Remember to use the free function to deallocate the structure once it is removed Be very careful of the following situations e What if the list is already empty Make sure your code detects this condition e What if the student you are removing is the only remaining student in the list What extra step s do you need to do in this situation e What if the student you are removing the first one in the list is the one currently being dis played If you do not change the current pointer it will be invalid 15 7 Summary Now that you have finished this lab you should understand the basic principles of linked lists and some of the reasons why they are used You should have investigated how linked lists can be handled in C and written some code to remove items from simple linked list This laboratory has only covered the basics of linked lists lab 16 will go into more depth making linked lists more useful Laboratory 16 Lists and Queues 2 16 1 Overview The last lab introduced the idea of storing structures by linking them together with references This is called a linked list This lab looks further at linked lists and examines some of the problems with the way in which linked lists were approached in the last lab You will be introduced to a more sophisticated form
252. son will be drawn It should also take a parameter which specifies the colour in which the stick person should be drawn e drawing the projectile path This function should have two parameters which specify the start ing point for the projectile in screen coordinates Place these functions under the main function in your source file You will need to define a prototype for each function If you do not know how to do this ask one of the demonstrators for help 5 7 2 Allowing Control of the Launch Angle Currently the stick person always throws the object at 45 because the horizontal and vertical velocities are equal You are now going to change the program so that the user can choose the launch angle of the object between 0 and 90 The velocity that the user specifies should be treated as the initial velocity of the object This velocity needs to be resolved into horizontal and vertical components These components can be calculated by treating the problem as a right angled triangle 98 Computer Programming Using C Revision 1 3 y component vy Velocity x component vz The x and y components can therefore be calculated using the sine and cosine of the launch angle 6 Uz vcos 0 5 1 vy usin 0 Exercise 5 9 Allowing the User to Choose the Launch Angle Alter your program to allow the user to type in the launch angle as well as the initial velocity before the graphics window appears The us
253. st Pointer gt NULL NULL lt Structure NULL gt NULL Finally both the first pointer and the last pointer should be set to reference the new structure First Pointer Last Pointer NULL gt NULL The structure has been successfully added to the list 16 4 2 Removing from a Double Linked List This section will look at the steps involved in removing a structure from a double linked list We will examine each of the four different situation under which this can occur in turn each of them has strong similarities to the steps involved in adding structures to the list Removing from the Head of the List The steps involved in removing a structure from the head of the list are e Set the first pointer to reference the next structure in the list e Set the previous pointer of the next structure in the list to be NULL e The structure is no longer part of the list its memory can be deallocated Removing from the Foot of the List The steps involved in removing a structure from the foot of the list are e Set the last pointer to reference the previous structure in the list e Set the next pointer of the previous structure in the list to be NULL e The structure is no longer part of the list its memory can be deallocated Revision 1 3 Computer Programming Using C 211 Removing from the Middle of the List The steps involved in removing a structure from the middle of the list are very simil
254. st of this lab looks at how you can implement a linked list in C 15 6 A Linked List Example The lab15 project is an example of how to construct a program which uses linked lists The program stores student details in a very similar way to the programs you worked with in lab 11 Copy the project and open it in the IDE You will find that it is made up of the following files gF 200 Computer Programming Using C Revision 1 3 e lab15 c contains the main function as well as the create_student function which creates a new student structure and fills in the details and the query_remove function which asks the user if they really want to remove a student from the list e display c contains the display student function which displays the currently selected stu dent and the display menu function which displays the simple user menu e display h contains prototypes for the functions in display c e list c contains functions for handling the actual linked list e list h contains prototypes for the functions in list c e types h contains type definitions for the two structures used in the program A screen shot of the lab15 program running is shown below ca H clab lab15 Debug lab15 exe Student Database Family Name Smith Given Name John Year of Birth 1986 Course Code 618 Up Previous Student Left First Student Right Last Student Down Next Student lt a gt A
255. string by writing to it The string is pre specified so it may be in memory which you are not allowed to write to For example you should not do the following message 5 1 If you want to be able to change the message you must put its contents into an array like this char message It s a long way to Tokyo n 176 Computer Programming Using C Revision 1 3 This will allocate writeable memory especially for the message and copy the message into it You can now change its contents Exercise 13 2 Investigating Strings as Pointers Open the lab6b project This project does some operations on a word that you enter It should count the length of the word and then reverse the characters in the word and display it Currently the reversal operation takes place in the main function e create a function called reverse_st ring which reverses the string that you give it e for both the reverse_st ring function and the string_length function change the proto types so that the string parameters are declared as pointers rather than arrays So your prototypes should be int string_length char string and void reverse_string char string You should find that declaring these parameters as pointers rather than arrays makes no difference to the operation of your program However when handling strings it is far more common to use the pointer notation than the array notation 13 4 Allocating Memory In th
256. student and stores them ina structure Write a separate function which will write the details of that student to a file The student details should all appear on the same line in the file separated by commas The lab17b project is another near empty template Basing your lab17b program on lab17a write a program which uses a separate function to read the details of a single student in from the file that was written to by the lab17 program The program should display the details it reads in Do not alter the lab17a program you need this in lab18 You might like to copy some of your code from the lab11 project to make this task easier Exercise 17 7 Adding Save and Load Functionality to a Program If you have been following the graphics option open the graphics3 project if you have been following the music option open the music3 project Each of these programs use an array of structures to store either a drawing in the case of the graphics option or a musical sequence in the case of the music option Based on the exercises you have done in this lab add functionality to your program to allow the user to save the contents of the array to a file or to load all the information from a file into the array This will allow a user to save and then reload their drawing or sequence 17 6 Summary Now that you have finished this laboratory you should understand how to carry out basic file
257. suming that there is no air resistance The initial velocity of the object as it comes out of the stick person s hand can be resolved into horizontal and vertical velocities These act along Revision 1 3 Computer Programming Using C 65 the x and y axes respectively The only force acting in our simple world is that of gravity Therefore there are no forces acting in the x direction and the horizontal velocity will remain constant There is one force in the y direction gravity The position in graphics coordinates of our object is P Pao Vat 3 1 Py Py Vyt gt 2 3 2 where e Pz Py is the current position of the object e Pro Pyo was the initial position of the object Vz was the velocity with which the object was thrown in the x direction in ms V was the velocity with which the object was thrown in the y direction in ms e gis the gravitational pull 9 81ms e tis the time in seconds For simplicity we will treat each pixel in the graphics window to be a metre wide just for the purpose of these equations The exact scale relationship between the graphics window and reality is not important We must now think about how these equations should be translated into a C program The best way to get a good graphical output is to find the height of the projectile in graphics y coordinates for every x position For example the following code would work time pos_x initial_pos_x vel
258. t Rebuild the project and try stepping through the code What value is displayed on the screen What is the value of count after the printf line has executed Replace the post increment operator with a pre increment operator so that the lines read count 5 printf count d n count How is that different You can remove these lines of code from the lab3a project when you have finished investigating them The increment operators are often useful for writing more compact C code They are most often used in for loops but can be used in many other places You should take great care when using shorthand operators as sometimes they make the purpose of code a lot less clear when it is read Exercise 3 4 A Simple for Loop Edit lab3a to create a program which always counts up from zero up to the number that the user entered You should only need to make very small changes to the lab3a code If you do not understand how to do this ask one of the demonstrators for help Revision 1 3 Computer Programming Using C 63 Syntax Shorthand Operators H H a y C specifies a set of shorthand operators that allow you to write more compact C code They are often especially useful in loops The most useful of these operators in loops are the pre and post increment and decrement operators variable variable variable variable The increment operator is equiva
259. t View Favorites Tools Help de Back p a Search Folders 3 us E X A Ea 314 Floppy Local Disk C Compact Disc w2k on pdm104 on My Computer A D userfsiSta userfs M Select an item to view its description 2 E 3 Displays the files and folders on your NDriveon Teaching on Control Panel computer lore amp y csrv ad yor See also My Documents Your N Drive My Network Places Network and Dial up Connections 8 objects My Computer e Double click on the icon for the N drive to view its contents Then double click on the following folders to navigate your way to the projects folder course elec examples c projects You should have a window like the following As an aside this navigation is often written as a path in the following way N course elec examples c projects amp projects 5 x File Edit Yiew Favorites Tools Help Back E Bsearch Gyrolders 4 US GE X wy Edy a lab11 lab13 projects D ca This folder is Online a o Select an item to view its description See also My Documents My Network Places My Computer D o co co D 16 object s O bytes fox Local intranet YA e Using the right hand mouse button click the folder that corresponds to the project you want to copy In this example we are copying the project lab1 Select the Copy item f
260. t a couple of hints You should use a loop to work through all the x coordinates that you need to Before the loop you should use moveto to set the current location you can then use 1ineto inside the loop to draw all the lines that will make up the path of the object A suitable do while loop would look something like this moveto initial_pos_x initial_pos y do time pos_x initial_pos_x vel_x pos_y int initial_pos_y vel_y time gravity time time 2 lineto pos_x pos_y pos_xt while pos_x Revision 1 3 Computer Programming Using C 67 You will notice that part of the while condition from this loop is missing where the is You will have to think about this for yourself You should also be aware that moveto and lineto functions are expecting integer numbers of type int as arguments If your variables are of type double they have to be converted by putting int before the variables that are arguments to these functions The conversion between double and int types is built in to C and is called a type cast You can see a type cast being carried out in the assignment statement for pos_y Exercise 3 6 Drawing the Projectile Path Using the information and hints you have been given add to your graphics1 project to draw the path of an object thrown from the stick person s hand The object path must not go underground If you use the standard value for gravity 9 81ms y
261. t character is the null character Call your new string_length function from within the ma infunction so that you can display the length of the word that the user enters If you don t understand how to do this ask one of the demonstrators for help Exercise 6 6 Character Array Handling Add to lab6b to add some code into the main function which copies the characters from the string_data array into another array but in reverse order You will need to use the length of the string which you determined in your string_length function to do this Display the reversed string using printf You must make sure that the new string you create the reversed copy has a null termination character in the right place If you don t understand how to do this ask one of the demonstrators for help 6 6 Forming Strings Using sprintf Sometimes you want to form a more complicated string which will be stored in a character array rather than displayed on the screen The sprintf function works exactly like printf except that rather than displaying the string it makes onto the screen in places the result into a character array which you specify For example look at the following code snippet char number_string 10 int an_integer an_integer 20 sprintf number_string Sd an_integer 114 Computer Programming Using C Revision 1 3 You can see that the sprintf function call looks very like a printf function call except that
262. t just integers You will need to change the type of the number_entered variable and the place holders in both the scanf and printf functions Rebuild and execute the program to check that it works 2 3 Making a Decision Conditional Statements We are now going to use a conditional statement to make a decision about which part of your program will execute depending on the number that the user enters We will do this using an if statement Change your lab2 program to remove the second printf line the one that displays the value back Se to the user and replace it with the following lines if number_entered gt 10 printf That number is bigger than ten n 42 Computer Programming Using C Revision 1 3 Try building and executing the program After you have entered the number it should tell you whether the number is bigger than 10 When you are satisfied that it works you may have to run it a few times add another two lines after the if part to add an else condition like this if number_entered gt 10 printf That number is bigger than ten n else printf That number is smaller than ten or equal to ten n Build your program and execute it a few times to test it with different numbers Exercise 2 2 Understanding Conditionals Use the debugger to try stepping through the program you have just written with the if statement in it Where does the flow of execution the yellow arrow go e for n
263. t might be suitable for your program e when each data item is represented by a structure if a data item is just a number an array is likely to be more efficient e when you need to be able to store anything from just a few data items to a large number e when you need to be able to add data items into the middle of a list and remove them or if you need to be able to change the order of data items easily e if the list will be very big the amount of memory an array would need would be very big and the computer would have to allocate it all in one chunk with a linked list the memory can be allocated in smaller pieces which is easier to accommodate The largest drawback with linked lists even double linked lists is that you cannot simply ask for the nth data item You must work through the list n times from the beginning or the end Arrays do not have this problem The property of being able to get to the nth data item immediately is called random access You may have noticed that the easiest way to handle single linked lists is to add and remove to from the head of the list This means that single linked lists as most appropriate in situations where the storage will be used in a LIFO fashion If FIFO type storage is required a double linked list is more appropriate 212 Computer Programming Using C Revision 1 3 16 6 Summary Now that you have finished this lab you should be able to work with both single and double linked lists Y
264. t notation is easier to read and is almost always used in place of the second Syntax Pointer to Structure Member Access Operator me The gt is used for accessing the member variables of a structure to which you have a pointer As in struct_pointer gt member For example my_ struct gt some_value Accesses the member variable some value from the structure which is referenced by the pointer variable my_struct This is directly equivalent to my_struct some_value Revision 1 3 Computer Programming Using 171 Exercise 12 7 Using Pointers with Structures Open the program that you were working on in lab 11 as part of your option This will be graph ics3 if you are were working on the graphics option or music3 if you were working on the music option Both these programs have a loop in the main function which accepts values from the user to put into a structure in the array Create a separate function which accepts a pointer to a structure It should be this function which prompts the user for values and places them in the structure The function prototype for those doing the graphics option might look something like this void get_line_values line_type new_line For those doing the music option it might look something like this void get_note_values note_type new_note You will have to use the reference operator when you call the function and the gt operator Ex
265. the array has space for is specified as a number in square brackets size When the array variable is used an integer must be included specifying the index of the element which is being referenced This index is called a subscript Subscripts are numbered starting from zero For example an_integer_array 6 is the integer value which occupies the 7th element in the the array called an_integer_array Revision 1 3 Computer Programming Using C 105 6 3 Working with Arrays You are now going to try using arrays in a program The lab6 project uses arrays to collect informa tion The program asks the user for the heights of up to ten people and then displays the mean height calculated from the data that were entered The heights that the user enters are stored in an array It would be very difficult to produce a program like this without using arrays Copy the lab6 project and open it in the IDE Try building and executing the program Test it out a few times to make sure you are familiar with what it does The source code for lab6 is shown below x A program to demonstrate arrays C Programming laboratory 6 include lt stdio h gt Function prototypes void welcome_message void double mean double values int num values x x Program starts here int main void Declare an array which can store up to 10 doubles x double data_values 10
266. the beginning of the list and then move it link by link through the list We will stop when pointer A is equal to the current pointer Every time pointer A is moved on one link pointer B is altered to be one behind it When pointer A reaches the current pointer B will reference the structure that comes before it We will now look at an example of how to do this in pseudo code set pointer_a to equal first_pointer set pointer_b to be NULL loop while pointer_a does not equal current_pointer and pointer_a is not NULL set pointer_b to equal pointer_a set pointer_a to equal the next structure after pointer_a end loop When the loop exits point er _b will reference the structure before the one referenced by the current_pointer In two situations pointer_b will be equal to NULL e the structure referenced by the current_pointer is the first one in the list in this case there is no structure before it e for some reason perhaps there is a bug elsewhere in the program the structure referenced by the current_pointer is not actually part of the list This method is very similar to the one used in the list_clear function in the lab15 project The list clear function goes through the whole list and deallocates the memory for all of the structures on the list It is called when the program ends to make sure that all dynamically allocated memory is freed Exercise 16 1 Finding the Previous Item in the List In the
267. the lab script are easy to find they have a picture of two gears next to them in the margin Like this There are two other kinds of special box e syntax boxes which tell you information about how to form valid statements in the C language syntax boxes look like this Syntax Some Syntax cas syntax GOSS MEWS o and the description of the syntax goes here e function boxes which tell you how to use C language functions function boxes look very similar to syntax boxes Function Reference A Function which does something the function goes here and the description of the function goes here Don t worry that you don t know what a function is yet this will become clear when you start the first lab The descriptions of both syntax and functions use some special symbols You should try and remember what these mean ready for when you meet your first syntax or function box e if something appears in square brackets like this then it means that it is optional e if something appears in square brackets with a small n above and to the right of it like this then it means that it is optional and can be repeated as many times as you want Don t worry if this does not seem clear now just remember that when you meet the first syntax or function box you can look back at this section to help you understand the information Before You Begin Overview This section contain
268. the most appropriate for a given situation The graphics and music options allow you to use these new structures for carrying out repetitive tasks that would be difficult without loop structures 3 2 Repeating Statements Many Times It is often necessary to repeat parts of your program many times Sometimes you will know exactly how many times this will happen and other times you will not In C structures that repeat many statements are often referred to as repetition structures loop structures or just loops The most basic way to repeat a single statement lots of times is to use a while loop A while loop executes a single statement over and over again as long as a relational expression just like the ones you used in if statements is true while loops look like this while relational_expression statement Just like with i f statements you will often want to put lots of statements inside a while To do this you should use a compound statement in place of the single statement underneath the while clause This is what has been done in the lab3 example Copy the lab3 project then try building and executing it The source code for lab3 c is shown below x A program to demonstrate the use of the while statement C Programming laboratory 3 58 Computer Programming Using C Revision 1 3 include lt stdio h gt int main void x Declare a variable to store an integer number x int number_ente
269. the time the C preprocessor silently goes about its work every time you build your program for example stripping out comments as mentioned above Sometimes you might want to communicate with the preprocessor directly This is done by including preprocessor commands or directives in your program All preprocessor directives begin with the hash or sharp symbol Preprocessor directives are not statements so they are not followed by a semicolon You have already used one preprocessor directive many times include For example include lt stdio h gt You might have noticed that there are two kinds of include directive include lt filename gt and include filename We will see what the difference is between these forms in a moment In common with most preprocessor directives the include directive does not do anything very complicated When the preprocessor sees a include directive it looks for the file that have specified for example stdio h When it finds the file it simply takes all of the text out of the file an inserts it into your source file in place of the include directive It does not try and process anything in the file or try to understand it in any way That is the compiler s job The difference between enclosing the filename in angle brackets like this lt stdio h gt and quotation marks like this st dio h is in where the preprocessor looks to find the file you have specified e Ifthe filename is
270. there is a new first argument The first argument to sprintf is the string variable that results will be placed into After the sprintf statement executes the string number_string contains the characters 2 0 and 0 Function Reference sprintf Forming strings using print f like placehold ers abate SBYSWEIIMICIE Conr siria wencaiclole Chea rormac SCH ooo e g sprintf number_string d int_variable sprintf answer_string The answer is d integer_answer num_chars sprintf display_string lf double_variable The sprintf function works like the print function except that instead of outputting its results onto the screen it places them into the character array string_variable It is called in exactly the same way as printf but with an extra first argument string_variable sprintf takes at least two arguments but like print it can take more depending on how many variables you want to include e string_variable is the character array which will receive the output of the sprintf func tion as a string e format_string is a string containing placeholders just like with printf e after the first two arguments where the is you should include variables whose values will be substituted for the placeholders in the format_st ring The placeholders you will use most often are e Sd for integer int variables e 1f double variables e Sc for single characters char e
271. thms conform to the data conventions identified in the previous section The main function is responsible for carrying out most of the program s functionality It calls the other functions whenever necessary to display the welcome message and reset the graphics window The most important role of the main function is the processing of key input from the user and the drawing of lines in the graphics window The main function uses four variables Variable Range C Type Description curr_x 0 640 int The x coordinate of the current drawing location curry 0 480 int The y coordinate of the current drawing location leave Oorl int 0 indicates that the program should continue run ning 1 indicates the program should finish key gt 1 e C q Q int The number of the key that was pressed by the user The structure for the main function algorithm is as follows display welcome messag Zero key press from the user was an arrow key or e that the position does not fal initialise graphics window set initial set leave to b begin loop get a TELE if it was c check if it does if the key was an arrow key draw a position to be centre of screen adjust so that it is within the window set current position correctly set the current position to be the centre of screen ll off the edge of the window line to the new current position Revision 1
272. ties e Select the item which says Map Network Drive A dialog box will appear Fill in the details exactly as shown in below and then click Finish Map Network Drive Windows can help you connect to a shared network Folder and assign a drive letter to the connection so that you can access the Folder using My Computer Specify the drive letter for the connection and the Folder that you want to connect to Drive fr Folder Wlore NDrive y Browse Example server share IV Reconnect at logon Connect using a different user name Create a shortcut to a Web folder or FTP site Cancel Creating a Folder For Your Work Itis a good idea to have a folder that will be used for all of your work during the C Programming course You will only need to create this folder once Double click on the My Documents icon on your desktop My Documents e A window like the following should appear Revision 1 3 Computer Programming Using C 5 My Documents 3 oj x File Edit View Favorites Tools Help de Back E search LA Folders S te e xX Eee Bea aaa E Applications corel user files CyberLink exceed ni My eBooks My Documents This Folder is Online E Select an item to view its description My Music My Pictures paradox hpothbO dat hpothbO tif Outlook pst Stores and manages documents x See also My Network Places Outlooki pst My Computer 13 objects
273. time_to_drive time_to_tokyo int average_speed Set the values of some of the variables Set distances in kilometres distance_to_tokyo 9720 16 Computer Programming Using C Revision 1 3 distance_to_airport 120 Set speeds in kilometres per hour speed_of_plane 1200 speed_of_car 100 x Calculate time taken to get to Tokyo x time_to_fly distance_to_tokyo distance_to_airport speed_of_plane time_to_drive distance_to_airport speed_of_car time_to_tokyo time_to_fly time_to_drive Calculate the average speed average_speed distance_to_tokyo time_to_tokyo return 0 We will now go through this code a line or two at a time Make sure that you understand it before continuing The first important thing to notice is that everything between and is a comment This means that itis ignored Syntax Comments eS E Comments are used for adding text to a source file which will be ignored by the compiler This is very useful for adding notes which will remind you about what a particular part of your program is supposed to do In Microsoft Visual Studio when you type a comment the editor will understand and colour it green The different colour helps you see easily which parts of your program are comments are which are not It is good programming practice to comment your programs well A good rule of thumb when writing comments is to write them for someone wh
274. tion Make sure that each decision you take is fully justified Exercise 8 4 Implementing Your Design Addition Follow your design and implement the additions you have just made How easy is it to follow your design Are you having to correct design mistakes whilst you program Do you think that you missed anything in your design 8 4 Music Option This design takes the example of a simple piece of software intended to make the QWERTY computer keyboard behave like a basic musical keyboard with only one octave 8 4 1 Specification The program is required to e allow the user to play any note from an octave e use the octave that starts on middle C each note should be activated from a key press on the QWERTY keyboard each note should be played for a short but fixed amount of time e allow the user to exit at any time Additionally it would be desirable if the program e uses keys on the keyboard that roughly correspond in layout to a musical keyboard e is easy and straightforward to use 8 4 2 Design The design will be split into three stages the user interface design a structural design and an algorithm design This process roughly corresponds to a top down design approach which starts from what the program should appear to do and works towards the question of how that functionality should be achieved 136 Computer Programming Using C Revision 1 3 User Interface Design The program wil
275. to C Copy the lab8 project You should find that the lab8 c source file is completely empty This is ready for your own code Exercise 8 1 Implementing the Design Implement the SketchPad program according to the design You will need to choose appropriate C statements that match with the pseudo code You will also need to make sure that you include the correct header files Exercise 8 2 Checking Your Implementation Test your implementation to make sure that it works Does it do what you expected it to Try out an implementation that a friend has done you could let them try yours How similar is it If it is different why is it different If a design is good then different implementations of it should be indistinguishable to a user Do you think the design could be improved If so how 8 3 4 Extending the Design You now have the chance to add to the design Although you are not producing a software report for this program you should make some notes as if you were writing a proper design This gives you the chance to practice writing a small part of a design Revision 1 3 Computer Programming Using C 135 Exercise 8 3 Adding to the Design Imagine that the specification contained an extra point The program is required to e allow the user to change between red green blue and white drawing colours Make notes on how you would amend the design to meet this new part of the specifica
276. tring2 the function returns a number greater than zero e if stringl matches string2 the function returns zero strcmp performs a case sensitive comparison strcmpi performs a case insensitive comparison Both the strcmp and strcmpi functions are defined in string h Exercise 18 2 Sorting a Linked List Based on Strings Alter your lab15 program to add a Sort option to the menu When the user selects this option the program should sort all the students in the linked list according to their family name You should use a bubble sort for this 18 3 Introducing Recursion A recursive function is a function which calls itself A function which calls itself usually causes some of the code in that function to be run a second time By calling itself a recursive function is forming a loop just like the while or for loops you have used on this course To differentiate the two types of looping using a while or for type loop which will occur within a function is called iteration Recursion is an alternative way to produce a loop in a program and any iterative program can be re written as recursive and vice versa In fact there are some programming languages that do not have Revision 1 3 Computer Programming Using C 223 any way of doing iteration In these languages the only way to produce a loop is using recursion o Copy the lab18 project and open it in the IDE The source code for the lab18 c f
277. umbers greater than ten e for numbers less than ten When the yellow arrow reaches a scanf statement it will wait until you enter a number before it will continue To enter the number you must make sure that the window in which your program is actually executing it will have a black background is at the front An if statement makes a decision based on the part that is in brackets The part in brackets is called a relational expression It compares things using relational operators such as greater than gt and less than lt to obtain an answer that is true or false The words if and else are treated specially by C it uses them to recognise that you want to do something conditionally Words that are treated specially in this way are called keywords because they are treated specially they cannot be used for variable names You will meet many more keywords as part of this course Revision 1 3 Computer Programming Using C 43 Syntax Relational Operators and Expressions lt gt l lt gt Relational operators allow you to compare things such as the value of variables and numbers or characters A simple relational expression compares two things and uses one relational operator iteml relational_operator item2 The relational operator can be any one of the following e lt less than e gt greater than e equal to e not equal to e lt less than or equal to e gt greater than or equa
278. ure which references the structure that comes before it in the list Each structure then has both a next pointer and a previous pointer This is depicted in the diagram below First Structure Structure Structure Structure Previous Pointers Next Pointers Last Structure The previous pointer can be used to travel in the reverse direction along the list For a single linked list the next pointer of the last structure in the list had the special value NULL to indicate that it was the last structure in the list In a double linked list the first structure has its previous pointer set to NULL in a similar way This is shown in the diagram below 206 Computer Programming Using C Revision 1 3 0x12345678 0x12345678 first 0x23456789 0x34567890 E 0x45678901 Given Name Year of Birth Course Code Next Pointer Previous Pointer Given Name Year of Birth Course Code Next Pointer Previous Pointer Given Name Year of Birth Course Code Next Pointer Previous Pointer Family Name Given Name Year of Birth Course Code Next Pointer Previous Pointer Family Name Family Name Family Name Smith John 1986 610 0x23456789 NULL Doe Jane 1985 600 0x34567890 0x12345678 Bloggs Fred 1982 606 0x45678901 0x23456789 Jones Francis 1974 636 NULL 0x23456789 A list like this is a lot more flexible but is
279. ures or pointers 143 Stacks LIFO Buffers Imagine you have a collection of blocks like a child s building blocks Each block has a number on it and represents an item of data that you might want to store A LIFO buffer would be represented by stacking these blocks one on top of another In this diagram the last block to be added to the stack was number 86 This is next block we may take away The last block we added to the stack is the first we can take away this gives the stack its name last in first out We can create a LIFO buffer using an array We can use a variable to tell us which element in the array is the next free one For example if we create an array of integers called buffer to use as a stack we can represent its contents using the box diagrams used in previous labs To make the array work as a stack we must keep track of the location of the next free slot In the situation shown in the diagram above the next free element in the array is buffer 5 so we would store the number 5 in a variable The next free location is usually called the top of the stack In this case we could have buf fer_top variable which is set to 5 see the next diagram Revision 1 3 Computer Programming Using C 185 ffer 7 5 butter top ffer 6 ffer 4 ffer 1l ffer 0 To add a new item of data we must place the data in the next free location in the array The next slot is buffer buffer_top
280. ware reports These points should reinforce the material you have covered in the lectures Each of the sections below is intended to reflect a section of your software report 8 5 1 Requirements The Requirements section should state the problem you have been given in its entirety You can imagine that the problem you have been given is a problem from a customer or client Quite often you will have requirements that are not explicitly stated in the problem In your case these requirements arise because you are doing a course on C programming Even though these requirements are implicit you should still state them They should include e the fact that you are expected to use the C programming language Revision 1 3 Computer Programming Using C 141 e the platform that you are expected to program for a PC running Microsoft Windows e the graphics or MIDI library you are expected to use 8 5 2 Analysis Your Analysis section should take the Requirements section as its starting point You should then at tempt to analyse the requirements to extract more information from them This is where you should flesh out the requirements with assumptions of your own if you have to The most important rule is that when you are doing an analysis you must treat the problem as a black box Treating something as a black box means that you should only be concerned with the the problem itself and its effects not how you will solve the problem You are a
281. which has the following path h clab labl debug labl exe Revision 1 3 Computer Programming Using C 21 SA You can look for it if you like The easier way is to use the Execute labl exe option on the Build gF menu Click on that option now You should find that a new window appears which is black and contains says Press any key to continue That means that your program has run and has already finished Very unimpressive so far You should have noticed from the program code that there are no statements telling the computer to display any information to the screen So it doesn t When you are writing a C program the computer will not do anything that you haven t told it to do Sometimes that is useful other times less so In order to find out whether your program is working or not and whether you understand what it is trying to do we are going to look inside the program whilst it is running This process is called debugging as it is usually used to try and find errors or bugs in your program and remove them The debugger is built in to the IDE We will be using two of its most important features e stepping which allows you to execute your program a line at a time while the editor shows you which line will be executed next e inspecting which allows you to look inside variables to find out what their values are whilst the program is running po To begin stepping through your program select the menu item
282. x pitch 60 We will play the note on MIDI channel 1 x Channel 1 x The note will have a medium velocity volume x velocity 64 x Play an octave s worth of chromatic scale x for offset 0 offset lt 12 offset Start playing a note x midi_note pitch offset channel velocity x Wait so that we can hear the note playing pause 400 x Turn the note off x midi_note pitch offset channel 0 return 0 Try compiling and running the program Does it sound how you expected it to sound Make sure you understand the for loop before continuing Exercise 3 9 Adding to the Chromatic Example Add to the music2 code to make it complete two octaves of ascending chromatic scale before descending back down chromatically to the starting note Revision 1 3 Computer Programming Using C 69 3 6 2 Whole Tone Scales A whole tone scale ascends in steps of whole tones in MIDI note numbers this is increments of two Composers like Debussy used whole tone scales to create a smooth dreamy effect which is often used in films to denote misty or underwater scenes Exercise 3 10 Playing a Whole Tone Scale Alter the code you have just created to play two octaves of ascending then descending whole tone scale Exercise 3 11 Using Whole Tone Scales By altering the code you have just created produce a program which plays four notes of a whole tone scale
283. y are useful If you need any help ask one of the demonstrators Include the correct preprocessor directives to make a sentry in each of your header files Your pro gram should still build and execute correctly 126 Computer Programming Using C Revision 1 3 7 5 Good Programming Practice Some More Tips This course has stressed many times the importance of creating source code that is easy to read and understand The best way to achieve this is e structure your code logically into functions which allow for reusability e structure your functions logically into different source files e use header files so that your source files are easily reused and are not cluttered with prototypes e document your source code with plenty of comments that are aimed at someone who understands C but does not necessarily understand how your program works You can make your easy to read through careful use of indentation Indentation is about changing where a line of code in your source file has its left hand edge It is very useful for making the structure of code inside functions clear You should control where the left hand edge of your lines of source code are using the Tab key Whenever you start a new structure like an if statement or a while loop you should indicate which lines are part of this structure by moving the lines to the right by inserting a tab character at the start of each line For example an if statement should alw
284. your own Remember that every statement in C ends with a semicolon e you will need to add two printf lines to display the percentage results Ask the demonstrators for help if you do not understand how to do this Exercise 1 5 The Return Code If you step through your program in the debugger or run it in the debugger but not if you choose the Execute command after your program has finished the output window contains the text The program H clab labl Debug labl exe has exited with code 0 0x0 If you change the last line of your program so that return 0 becomes return 20 for example what happens to the message in the output window after your program has finished running You can change this number to be whatever you like but it must be an integer 26 Computer Programming Using C Revision 1 3 1 7 Graphics Option You should only begin this section if you have chosen to do the graphics option i e if you are a non Music Technology student or if you have chosen to do the music option but have already completed that section The section for the music option begins after this one Section 1 8 on page 32 As an example of how to use C we are going to investigate graphical output Although this is not strictly part of the C language the principles are important for all C programming Producing graphical output in Windows is quite complicated so this laboratory course uses a set of functions
285. ys as always being passed by reference The project lab13 contains a skeleton for a program which might use an array Copy this project nd open it in the IDE Based on the very simple programs you used in laboratory 12 create a program which demonstrates that arrays are effectively always passed by reference You can make the program as simple or complicated as you like 13 3 More About Strings In lab 6 you saw that character strings are also arrays arrays of type char Each element is a character and the last element in the string is always the null character 0 Since string variables are arrays they are also pointers You will often find that functions that operate on strings expect a parameter of type char x i e a character pointer For example the prototype for the standard C function strlen is as follows int strlen charx str The strlen function calculates the length the string it was passed by finding the null termination char acter You wrote a function to do this in lab 6 You can assign strings to pointers that are specified in your program like this char message message It s a long way to Tokyo n You could then display the message using a printf statement like this printf message You can access individual characters of the message using the array subscript square brackets for ex ample messagel 5 would be equivalent to the character a However you can not change the

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