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Chapter 2 Introduction to the C Language

1. define SPACE define BANG define DBL_QTE define QUOTE define COMMA define COLON TABLE 2 14 Examples of Defined Constants Data Hiding In Structure of a C Program in Section 2 2 we discussed the concept of global and local variables We pointed out that anything placed before main Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 80 Section 2 9 Software Engineering was said to be in the global part of the program With the exception of data that must be visible to other programs no variables should be placed in this section One of the principles of structured programming states that the data structure should be hidden from view The two terms you usually hear in connection with this concept are data hiding and data encapsulation Both of these principles have as their objective protecting data from acci dental destruction by parts of your program that don t require access to the data In other words if a part of your program doesn t require data to do its job it shouldn t be able to see or modify the data Until you learn to use
2. This example has three conversion specifications but only two addresses Therefore scanf reads the first two values and quits because no third address if found 4 int a 1 int b 2 int c 3 scanf d d amp a amp b amp C printf d d n a by c 5 ak al input 5 10 3 output This example has only two conversion specifications but it has three addresses Therefore scanf reads the first two values and ignores the third address The value 15 is still in the input stream waiting to be read 2 8 Programming Examples In this section we show some programming example to emphasize the ideas and concepts we have discussed about input output EXAMPLE 2 2 Print Nothing Program 2 4 is a very simple program that prints Nothing PROGRAM 2 4 A Program That Prints Nothing 1 Prints the message Nothing 2 Written by 3 Date 4 5 include lt stdio h gt 6 7 int main void 8 9 Statements 10 printf This program prints n n t Nothing r1 return 0 12 main continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of
3. We recommend that you don t use non whitespace characters in the format string at least until you learn how to recover from errors in Chapter 13 However there are some uses for it For example if the users want to enter dates with slashes such as 5 10 06 the slashes must either be read and discarded using the character format specifica tion see the discussion of the assignment suppression flag in the later section Conversion Specification or coded as non whitespace in the format specification We prefer the option to read and discard them b Whitespace characters in the format string are matched by zero or more whitespace characters in the input stream and discarded There are two exceptions to this rule the character conversion code and the scan set see Chapter 11 do not discard whitespace It is easy how ever to manually discard whitespace characters when we want to read a character We simply code a space before the conversion specifica tion or as a part of it as shown below Either one works Se or S a Remember that whenever we read data from the keyboard there is a return character from a previous read If we don t flush the whitespace char acters when we read a character therefore we will get the whitespace from the previous read To read a character we should always code at least one whitespace character in the conversion specification otherwise the whitespace remaining in the input stream is read as t
4. ing and data hiding 29 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 30 Section 2 1 Background 2 1 Background C is a structured programming language It is considered a high level lan guage because it allows the programmer to concentrate on the problem at hand and not worry about the machine that the program will be using While many languages claim to be machine independent C is one of the closest to achieving that goal That is another reason why it is used by software develop ers whose applications have to run on many different hardware platforms C like most modern languages is derived from ALGOL the first lan guage to use a block structure ALGOL never gained wide acceptance in the United States but it was widely used in Europe ALGOL s introduction in the early 1960s paved the way for the develop ment of structured programming concepts Some of the first work was done by two computer scientists Corrado Bohm and Guiseppe Jacopini who pub lished a paper in 1966 that defined the concept of structured programming Another computer scientist Edsger Dijkstr
5. 11 Do not use commas or other characters in the format string for a scanf statement This will most likely lead to a run time error when the user does not enter matching commas or characters For example the comma in the following statement will create a run time problem if the user doesn t enter it exactly as coded scanf d d amp a amp b Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 82 Section 2 12 Summary 2 11 2 12 12 Unless you specifically want to read a whitespace character put a space before the character conversion specification in a scanf statement 13 Using an address operator amp with a variable in the printf statement is usually a run time error 14 Do not put a trailing whitespace at the end of a format string in scanf This is a fatal run time error Key Terms address list address operator ASCII binary stream block comment Boolean call character constant character set comment complex type constant conversion code conversion specification data encapsulation data hiding declaration definition derived types end
6. 32 33 34 Code the variable declarations for each of the following a a character variable named option b an integer variable sum initialized to 0 c a floating point variable product initialized to 1 Code the variable declarations for each of the following a a short integer variable named code b a constant named salesTax initialized to 0825 c a floating point named sum of size double initialized to 0 Write a statement to print the following line Assume the total value is contained in a variable named cost The sales total is oS ARRAKRARAAKRAKRAKRARARAARARAKRARAAAKRRAARNR Write a program that uses four print statements to print the pattern of asterisks shown below kkkkkk kkkkkk kkkkkk kkkkkk Write a program that uses four print statements to print the pattern of asterisks shown below KKK KKKK Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 90 Section 2 13 Practice Sets Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication ma
7. A format control string describes the data to be extracted from the stream and reformatted id Rather than data values as in the printf function scanf requires the variable addresses were each piece of data are to be stored Unlike the printf function the destination of the data items cannot be literal values they must store in the variables 3 With the exception of the character specification leading whitespaces are discarded 4 Any non conversion specification characters in the format string must be exactly matched by the next characters in the input stream We must be careful about extra characters in the control stream Extra characters in the control string can be divided into two categories non whitespace and whitespace Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 63 a Non whitespace characters in the control string must exactly match characters entered by the user and are discarded by the scanf after they are read If they don t match then scanf goes into an error state and the program must be manually terminated
8. ASCII for character is 34 ASCII for character is 92 ASCII for character is 39 EXAMPLE 2 5 Define Constants Let s write a program that calculates the area and circumference of a circle using a preprocessor defined constant for m Although we haven t shown you how to make calculations in C if you know algebra you will have no problem reading the code in Program 2 7 PROGRAM 2 7 Calculate a Circle s Area and Circumference 1 This program calculates the area and circumference 2 of a circle using PI as a defined constant 3 Written by 4 Date 5 Ae 6 include lt stdio h gt 7 define PI 3 1416 8 9 int main void 10 11 Local Declarations 12 float circ 13 float area 14 float radius continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 72 Section 2 8 Programming Examples PROGRAM 2 7 Calculate a Circle s Area and Circumference continued 15 16 Statements L7 printf nPlease enter the value of the radius 18 scanf f amp radius 19 20 circ 2 PI radius 21 area
9. PI radius radius 22 23 printf nRadius is 10 2 radius 24 printf nCircumference is 10 2f circ 25 printf nArea is 10 2f area 26 27 return 0 28 main Results Please enter the value of the radius 23 Radius is 23 00 Circumference is 144 51 Area is LOOL Sil EXAMPLE 2 6 Print a Report You are assigned to a new project that is currently being designed To give the customer an idea of what a proposed report might look like the project leader has asked you to write a small program to print a sample The specifi cations for the report are shown in Figure 2 22 and the code is shown in Program 2 8 IN Part Number Qty On Hand Qty On Order Price 031235 22 86 45 62 000321 55 is 122 00 028764 7 0 75 003232 10 91 End of Report NN Ca lt lt FIGURE 2 22 Output Specifications for Inventory Report Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 73 The report contains four fields a part number which must be printed with leading zeros the current quan
10. define that a function has no return value as we see in Chapter 4 It can also be used to define a pointer to generic data as we will see in Chapter 9 Integral Type The C language has three integral types Boolean character and integer Integral types cannot contain a fraction part they are whole numbers Boolean With the release of C99 the C language incorporated a Boolean type Named after the French mathematician philosopher George Boole a Bool ean type can represent only two values true or false Prior to C99 C used integers to represent the Boolean values a nonzero number positive or negative was used to represent true and zero was used to represent false For backward compatibility integers can still be used to represent Boolean Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 39 values however we recommend that new programs use the Boolean type The Boolean type which is referred to by the keyword bool is stored in mem ory as 0 false or 1 true Character The third type is character Although we think of
11. functions in Chapter 4 however you will not be able to provide this data hiding capability Nevertheless you should start your programming with good practices And since our ultimate objective is good structured programming we now formulate our first programming standard Programming Standard No variables are to be placed in the global area of a program Any variables placed in the global area of your program that is before main can be used and changed by every part of your program This is unde sirable and is in direct conflict with the structured programming principles of data hiding and data encapsulation Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 81 2 10 Tips and Common Programming Errors 1 Well structured programs use global defined constants but do not use global variables 2 The function header for main should be complete We recommend the following format int main void a If you forget the parentheses after main you will get a compile error b If you put a semicolon after the parentheses
12. you will get a compile error c If you misspell main you will not get a compile error but you will get an error when you try to link the program All programs must have a function named main 3 If you forget to close the format string in the scanf or printf statement you will get a compile error 4 Using an incorrect conversion code for the data type being read or writ ten is a run time error You can t read an integer with a float conversion code Your program will compile with this error but it won t run correctly 5 Not separating read and write parameters with commas is a compile error 6 Forgetting the comma after the format string in a read or write statement is a compile error 7 Not terminating a block comment with a close token is a compile error 8 Not including required libraries such as stdio h at the beginning of your program is an error Your program may compile but the linker cannot find the required functions in the system library 9 If you misspell the name of a function you will get an error when you link the program For example if you misspell scanf or printf your pro gram will compile without errors but you will get a linker error Using the wrong case is a form of spelling error For example each of the fol lowing function names are different scanf Scanf SCANF printf Printf PRINTF 10 Forgetting the address operator amp on a scanf parameter is a logic run time error
13. 214 156 142 scanf Sd dsd c amp a amp b amp cC amp d Note that a space between the 14 and the z would create an error because c does not skip whitespace To prevent this problem put a space before the sc code as shown below This will cause it to skip leading whitespace scanf Sd d d c amp a amp b amp cC amp d 2 2314 15 2 14 scanf ctd td sf ka amp D ECY Note the whitespace between the conversion specifications These spaces are not necessary with numeric input but it is a good idea to include them Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 67 3 14 26 25 66 scanf 2d 2d 2d 2d amp numl amp denl amp num2 amp den2 Note the slashes in the format string Since they are not a part of the conversion specification the user must enter them exactly as shown or scanf will stop reading 4 11 25 56 scanf d d d amp a amp b amp c Again we see some required user input this time dashes between the month day and year While this is a common date format it can ca
14. may be trademarks or registered trademarks of their respective manufactures and sellers 48 Section 2 6 Constants The character in the character constant comes from the character set supplied by the hardware manufacturer Most computers use the ASCII char acter set or as it is sometimes called the ASCII alphabet The ASCII charac ter set is shown in Appendix A C has named the critical character values so that we can refer to them symbolically Note that these control characters use the escape character fol lowed by a symbolic character They are shown in Table 2 6 ASCII Character Symbolic Name null character alert bell backspace horizontal tab newline vertical tab form feed carriage return single quote double quote backslash TABLE 2 6 Symbolic Names for Control Characters Integer Constants Although integers are always stored in their binary form they are simply coded as we would use them in everyday life Thus the value 15 is simply coded as 15 If we code the number as a series of digits its type is signed integer or signed long integer if the number is large We can override this default by specifying unsigned u or U and long 1 or L or long long 11 or LL after the number The codes may be combined and may be coded in any order Note that there is no way to specify a short int constant When we omit the suffix on a literal it defaults to int While both upper and lowercase codes are allowed
15. of file EOF escape character flag modifier Summary statements floating point type format control string function global declaration section header file identifier imaginary type include initializer integral type intelligent data name justification keyword Latin character set line comment literal logical data memory constant padding parameter parameter list precision modifier program documentation real type reserved word sign flag size modifier standard input standard output statement standard types statement section stream string string constant syntax text stream token type type qualifier variable width modifier LI In 1972 Dennis Ritchie designed C at Bell Laboratories 1 In 1989 the American National Standards Institute ANSI approved ANSI C in 1990 the ISO standard was approved _ The basic component of a C program is the function 1 Every C function is made of declarations definitions and one or more _J One and only one of the functions in a C program must be called main Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufacture
16. resulting text stream to the standard output monitor For example an integer 234 stored in the program is converted to a text stream of three numeric ASCII characters 2 3 and 4 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 55 and then is sent to the monitor What we see on the monitor is these three characters not the integer 234 However we interpret the three characters together as an integer value Figure 2 16 shows the concept Text Stream printf Integer Data Destination Program FIGURE 2 16 Output Formatting Concept Basic Concept The printf function uses an interesting design to convert data into text streams We describe how the text stream should be formatted using a format control string containing zero or more conversion specifications In addi tion to the conversion specifications the control string may contain textual data and control characters to be displayed Each data value to be formatted into the text stream is described as a sep arate conversion spe
17. symbols to represent a Boolean type The values are true and false As we mentioned before a Boolean value can have only one of the two values 0 false and 1 true We use the constant true or false in our program To do so however requires that we include the Boolean library stdbool h Character Constants Character constants are enclosed between two single quotes apostrophes In addition to the character we can also use a backslash before the char acter The backslash is known as the escape character It is used when the character we need to represent does not have any graphic associated with it that is when it cannot be printed or when it cannot be entered from the key board The escape character says that what follows is not the normal charac ter but something else For example n represents the newline character line feed So even though there may be multiple symbols in the character constant they always represent only one character A character constant is enclosed in single quotes Wide character constants are coded by prefixing the constant with an L as shown in the following example Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and
18. that they end up using them over and over It only takes a few minutes to document a program and it is always time well spent If nothing else it helps clarify the program in your mind Next look carefully at the formatting for the print statements Spacing is controlled by a combination of tabs and format code widths The double spacing for the end of Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 74 Section 2 8 Programming Examples report message is controlled by placing a newline command n at the beginning of the message in Statement 29 Finally note that the program concludes with a return statement that informs the operating system that it concluded successfully Attention to details even in small pro grams is the sign of a good programmer EXAMPLE 2 7 Printing The Attributes of a Complex Number A complex number is made of two components a real part and an imaginary part In mathematics it can be represented as a vector with two components The real part is the projection of the vector on the horizontal axis x and the imaginary part is the projection of the vect
19. their respective manufactures and sellers Chapter 2 Introduction to the C Language 69 PROGRAM 2 4 A Program That Prints Nothing continued Results This program prints Nothing EXAMPLE 2 3 Print Boolean Constants Program 2 5 demonstrates printing Boolean values As the program shows however while a Boolean literal contains either true or false when it is printed it is printed as 0 or 1 This is because there is no conversion code for Boolean To print it we must use the integer type which prints its stored value 0 or 1 PROGRAM 2 5 Demonstrate Printing Boolean Constants 1 Demonstrate printing Boolean constants 2 Written by 3 Date 4 5 include lt stdio h gt 6 include lt stdbool h gt 7 8 int main void 9 10 Local Declarations it bool x true 12 bool y false 13 14 Statements 15 printf The Boolean values are d d n x Y 16 return 0 17 main Results The Boolean values are 1 0 EXAMPLE 2 4 Print Character Values Program 2 6 demonstrates that all characters are stored in the computer as integers We define some character variables and initialize them with values and then we print them as integers As you study the output note that the ASCII values of the characters are printed The program also shows the value of some nonprintable characters All values can be verified by referring to Appendix A Copyright 2007 by Thomson C
20. to alert the user to a condition that needs attention These control characters are seen in Table 2 6 Conversion Specification To insert data into the stream we use a conversion specification that contains a start token a conversion code and up to four optional modifiers as shown in Figure 2 18 Only the field specification token and the conver sion code are required Minimum TA 7 FIGURE 2 18 Conversion Specification Approximately 30 different conversion codes are used to describe data types For now however we are concerned with only three character c Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 57 integer d and floating point These codes with some examples are shown in Table 2 10 Example short int int long int long long int float ie double 1 long double f a Size is discussed in the next section TABLE 2 10 Format Codes for Output The size modifier is used to modify the type specified by the conversion code There are four different sizes h 1 el 11 el el and
21. year 233 12 The tax is 233 12 this year ARRRAKRKRARARAARAKRARAARAARRAKRARARAN printf The tax is 308 2f this year 233 12 The tax is 00233 12 this year ARRRAKRRARARAARARARKRARRARARAARRARANR This example uses the zero flag to print leading zeros Note that the width is eight positions Three of these positions are taken up by the pre cision of two digits and the decimal point This leaves five positions for the integral portion of the number Since there are only three digits 233 printf inserts two leading zeros printf 8c Sa thy 23 h 23 ARRAKRARAKRAARAARAAAR In this example we want to print the data within quotes Since quotes are used to identify the format string we can t use them as print characters To print them therefore we must use the escape character with the quote which tells printf that what follows is not the end of the string but a character to be printed in this case a quote mark printf This line disappears r A new line n printf This is the bell character a n printf A null character 0kills the rest of the line n Chapter 2 Introduction to the C Language 61 printf nThis is it in single quotes n printf This is it in double quotes n printf This is the escape character itself n A new line This is the bell character A null character This is it in single quotes This is it in double quotes This is the es
22. 5 PROGRAM 2 9 Print Complex Number Attributes continued 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Local Declarations double complex x 4 4 T double complex xc Statements xc conj x printf sf sf tf f n creal x cimag x cabs x carg xX printf sf sf sf f n creal xc cimag xc cabs xc carg xc return 0 amain Results 4 000000 4 000000 5 656854 0 785398 4 000000 4 000000 5 656854 0 785398 EXAMPLE 2 8 Mathematics with Complex Numbers C allows us to add subtract multiply and divide two complex numbers using the same operators that we use for real numbers Program 2 10 demonstrates the arithmetic use of operators with complex numbers PROGRAM 2 10 Complex Number Arithmetic o N A UF WDN FB PRPrPrP RPP PP NYnDUBWNHHOLO Demonstrate complex number arithmetic Written by Date include lt stdio h gt include lt math h gt include lt complex h gt int main void Local Declarations double complex x 3 4 I double complex y 3 4 I double complex sum double complex dif double complex mul double complex div continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and com
23. Chapter 2 Introduction to the C Language In Chapter 1 we traced the evolution of computer languages from the machine languages to high level languages As mentioned C the language used exclusively in this book is a high level language Since you are going to spend considerable time working with the language you should have some idea of its origins and evolution In this chapter we introduce the basics of the C language You will write your first program which is traditionally known in C as the Hello World or Greeting program Along the way we will introduce you to the concepts of data types constants and variables Finally you will see two C library func tions that read and write data Since this chapter is just an introduction to C most of these topics are covered only in sufficient detail to enable you to write your first program They will be fully developed in future chapters Objectives To understand the structure of a C language program To write your first C program To introduce the include preprocessor command To be able to create good identifiers for objects in a program To be able to list describe and use the C basic data types To be able to create and use variables and constants in a program To understand input and output concepts as they apply to C programs To be able to use simple input and output statements UouvuoevovovUoo To understand the software engineering role in documentation data nam
24. II characters are now known as the basic Latin character set Gen erally speaking the wide character set is beyond the scope of an introductory programming text and is not covered in this text Integer An integer type is a number without a fraction part C supports four different sizes of the integer data type short int int long int and long long int A short int can also be referred to as short long int can be referred to as long and long long int can be referred to as long long C defines these data types so that they can be organized from the smallest to the largest as shown in Figure 2 9 The type also defines the size of the field in which data can be stored In C this is true even though the size is machine dependent and var ies from computer to computer short int int long int long long int FIGURE 2 9 Integer Types If we need to know the size of any data type C provides an operator sizeof that will tell us the exact size in bytes We will discuss this operator in detail in Chapter 3 Although the size is machine dependent C requires that the following relationship always be true sizeof short lt sizeof int lt sizeof long lt sizeof long long Each integer size can be a signed or an unsigned integer If the integer is signed then one bit must be used for a signed 0 is plus 1 is minus The unsigned integer can store a positive number that is twice as large a
25. L The h is used with the integer codes to indicate a short integer value the 1 is used to indi cate a long integer value the 11 is used to indicate a long long integer value and the L is used with floating point numbers to indicate a long double value A width modifier may be used to specify the minimum number of posi tions in the output If the data require using more space than we allow then printf overrides the width It is very useful to align output in columns such as when we need to print a column of numbers If we don t use a width mod ifier each output value will take just enough room for the data If a floating point number is being printed then we may specify the num ber of decimal places to be printed with the precision modifier The preci sion modifier has the format where m is the number of decimal digits If no precision is specified printf prints six decimal positions These six decimal positions are often more than is necessary When both width and precision are used the width must be large enough to contain the integral value of the number the decimal point and the num ber of digits in the decimal position Thus a conversion specification 5 The h code is a carry over from assembler language where it meant half word Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior per
26. a popularized the concept His letter to the editors of the Communications of the ACM Association of Com puting Machinery brought the structured programming concept to the atten tion of the computer science community Several obscure languages preceded the development of C In 1967 Martin Richards developed a language he called Basic Combined Program ming Language or BCPL Ken Thompson followed in 1970 with a similar language he simply called B B was used to develop the first version of UNIX one of the popular network operating systems in use today Finally in 1972 Dennis Ritchie developed C which took many concepts from ALGOL BCPL and B and added the concept of data types This path along with sev eral others is shown in Figure 2 1 ALGOL BCPL ALGOL 68 Pascal B ALGOL W Modula 2 Traditional Modula 3 g c99 ee FIGURE 2 1 Taxonomy of the C Language Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 31 What is known as traditional C is this 1972 version of the language a
27. actures and sellers Chapter 2 Introduction to the C Language 85 8 The code that establishes the original value for a variable is known as a n a assignment b constant c initializer d originator e value 9 Which of the following statements about a constant is true a Character constants are coded using double quotes b It is impossible to tell the computer that a constant should be a float or a long double c Like variables constants have a type and may be named d Only integer values can be used in a constant e The value of a constant may be changed during a program s execution 10 The conversion specification is used to read or write a short integer a c b 3d c bf d shad e 31f 11 To print data left justified you would use a in the conversion specification a flag b precision c size d width e width and precision 12 The function reads data from the keyboard a displayf b printf c read d scanf e write 13 One of the most common errors for new programmers is forgetting to use the address operator for variables in a scanf statement What is the address operator a The address modifier in the conversion specification b The ampersand amp c The caret d The percent 3 e The pound sign Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this p
28. ames their identifiers The concept of variables in memory is illustrated in Figure 2 11 Variable s identifier Variable s type char code ine i long long national_debt float payRate double pi Program FIGURE 2 11 Variables A variable s type can be any of the data types such as character integer or real The one exception to this rule is the type void a variable cannot be type void To create a variable we first specify the type which automatically speci fies it size precision and then its identifier as shown below in the definition of a real variable named price of type float float price Table 2 5 shows some examples of variable declarations and definitions As you study the variable identifiers note the different styles used to make them readable You should select a style and use it consistently We prefer the use of an uppercase letter to identify the beginning of each word after the first one although we do include examples using underscores Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 44 Section 2 5 Varia
29. an underscore In this way we make sure that our names do not duplicate system names which could become very confusing The last rule is that the name we create cannot be keywords Keywords also known as reserved words include syntactical words such as if and while For a list of the reserved words see Appendix B Good identifier names are descriptive but short To make them short we often use abbreviations C allows names to be up to 63 characters long If 2 One way to abbreviate an identifier is to remove any vowels in the middle of the word For example student could be abbreviated stdnt Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 37 the names are longer than 63 characters then only the first 63 are used Table 2 1 summarizes the rules for identifiers First character must be alphabetic character or underscore Must consist only of alphabetic characters digits or underscores First 63 characters of an identifier are significant Cannot duplicate a keyword TABLE 2 1 Rules for Identifiers You might be cur
30. and the monitor is known as standard output A terminal keyboard and monitor can be associated only with a text stream A keyboard is a source for a text stream a monitor is a destination for a text stream Figure 2 15 shows the concept of streams and the two physical devices asso ciated with input and output text streams Data Source Program Text Stream tput Text Stream monitor Data Destination FIGURE 2 15 Stream Physical Devices Formatting Input Output The previous section discussed the terminal as a text stream source and desti nation We can only receive text streams from a terminal keyboard and send text streams to a terminal monitor However these text streams often repre sent different data types such as integer real and Boolean The C language provides two formatting functions printf for output formatting and scanf for input formatting The printf function converts data stored in the program into a text stream for output to the monitor the scanf function converts the text stream coming from the keyboard to data values and stores them in pro gram variables In other words the printf and scanf functions are data to text stream and text stream to data converters Output Formatting printf The output formatting function is printf The printf function takes a set of data values converts them to a text stream using formatting instructions con tained in a format control string and sends the
31. as a decimal 75 The number as a float 0 000000 Projects 39 Write a C program using printf statements to print the three first letters of your first name in big blocks This program does not read anything from the keyboard Each letter is formed using seven rows and five col umns using the letter itself For example the letter B is formed using 17 B s as shown below as part of the initials BEF BBB I VR ey Wee Ag F BABE E BBB EEE FEEF BAB E E BABE E BBB EEEEE F This is just an example Your program must print the first three let ters of your first name Design your printf statements carefully to create Chapter 2 Introduction to the C Language 91 enough blank lines at the beginning and end to make your initials read able Use comments in your program to enhance readability as shown in this chapter 40 Write a program that reads a character an integer and a floating point number It then prints the character first using a character format speci fication c and then using an integer specification d After printing the character it prints the integer and floating point numbers on separate lines Be sure to provide complete instructions prompts for the user 41 Write a program that prompts the user to enter three numbers and then prints them vertically each on one line first forward and then reversed the last one first as shown in the following design Please enter three numbers 15 35 72 Your
32. ate a constant is to use the preprocessor command define Like all preprocessor commands it is prefaced with the pound sign The define commands are usually placed at the beginning of the program although they are legal anywhere Placing them at the beginning of the pro gram makes them easy to find and change A typical define command might be define SALES TAX RATE 0825 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 52 Section 2 6 Constants In the preceding example for instance the sales tax rate changes more often than we would like By placing it and other similar constants at the beginning of the program we can find and change them easily As the preprocessor reformats the program for the language translator it replaces each defined name SALES_TAX_RATE in the previous example with its value 0825 wherever it is found in the source program This action is just like the search and replace command found in a text editor The prepro cessor does not evaluate the code in any way it just blindly makes the sub stitution For a complete discussion of defined constants
33. bles fact maxItems separator Capital long national_debt separator underscore payRate separator Capital tax complex voltage code kind style see text ar Dr style see text TABLE 2 5 Examples of Variable Declarations and Definitions C allows multiple variables of the same type to be defined in one state ment The last two entries in Table 2 5 use this format Even though many professional programmers use it we consider it to be poor programming style It is much easier to find and work with variables if they are defined on sepa rate lines This makes the compiler work a little harder but the resulting code is no different This is one situation in which ease of reading the program and programmer efficiency are more important than the convenience of coding multiple declarations on the same line Variable Initialization We can initialize a variable at the same time that we declare it by including an initializer When present the initializer establishes the first value that the variable will contain To initialize a variable when it is defined the identifier is followed by the assignment operator and then the initializer which is the value the variable is to have when the function starts This simple initializa tion format is shown below int count 0 Every time the function containing count is entered count is set to zero Now what will be the result of the following initialization Are both count and
34. blocks of code that accomplish a task within a program One and only one of the functions must be named main The main function is the starting point for the pro gram All functions in a program including main are divided into two sec tions the declaration section and the statement section The declaration section is at the beginning of the function It describes the data that you will 1 Brian Kernighan and Dennis Ritchie The C Programming Language 2nd ed Englewood Cliffs N J Prentice Hall 1989 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 32 Section 2 2 C Programs be using in the function Declarations in a function are known as local decla rations as opposed to global declarations because they are visible only to the function that contains them The statement section follows the declaration section It contains the instructions to the computer that cause it to do something such as add two numbers In C these instructions are written in the form of statements which gives us the name for the section Figure 2 2 shows the parts of a simple C program We
35. brary file in the pointed brackets lt gt included in your program The name of the header file is stdio h This is an abbreviation for standard input output header file main The executable part of your program begins with the function main which is identified by the function header shown below We explore the meaning of the function syntax in Chapter 4 For now all you need to understand is that int says that the function will return an integer value to the operating system that the function s name is main and that it has no parameters the parame ter list is void Note that there is no punctuation after the function header int main void Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 34 Section 2 2 C Programs Within main there are two statements one to print your message and one to terminate the program The print statement uses a library function to do the actual writing to the monitor To invoke or execute this print function you call it All function call statements consist of the name of the function in this case printf followed by a parameter list enclo
36. cape character itself These examples use some of the control character names found in Table 2 6 Two of them give unexpected results In Output Example 11 the return character r repositions the output at the beginning of the current line without advancing the line Therefore all data that were placed in the output stream are erased The null character effectively kills the rest of the line Had we not put a newline character n at the beginning of the next line it would have started immediately after character 12 New example with multiple flags print 8 2f 0 8 2 0 8 2 1 2 2 3 3 4 1 20 0002 30 3 40 ARKRRAKRARAKRAKRARARAKRARARARARKRARARAARKRN This example uses multiple flags So that we can see the justification each value is enclosed in vertical bars The first value is printed left justi fied with the positive flag set The second example uses zero fill with a space for the sign Note that there is a leading space in the output This represents the plus value It is then followed by the leading zeros The last example demonstrates that the zero fill is ignored when a numeric value is printed with left justification Common Output Errors Each of the following examples has at least one error Try to find each one before you look at the solutions Your results may vary depending on your compiler and hardware l printf d d d n 44 55 44 55 0 This example has three conversion spe
37. characters as the letters of the alphabet a computer has another definition To a computer a character is any value that can be represented in the computer s alphabet or as it is bet ter known its character set The C standard provides two character types char and wehar_t char wchar t FIGURE 2 8 Character Types Most computers use the American Standard Code for Information Inter change ASCII pronounced ask key alphabet You do not need to memo rize this alphabet as you did when you learned your natural languages however you will learn many of the special values by using them The ASCII code is included in Appendix A Most of the personal mini and mainframe computers use 1 byte to store the char data types A byte is 8 bits With 8 bits there are 256 different values in the char set Note in Appendix A that ASCII uses only half of these possible values Although the size of char is machine dependent and varies from computer to computer normally it is 1 byte or 8 bits If you examine the ASCII code carefully you will notice that there is a pattern to its alphabet that corresponds to the English alphabet The first 32 ASCII characters and the last ASCII character are control characters They are used to control physical devices such as monitors and printers and in telecommunication systems The rest are characters that we use to com pose words and sentences All the lowercase letters are grouped tog
38. cification in the control string The specifications describe the data values type size and specific format information such as how wide the display width should be The location of the conversion specification within the format control string determines its position within the text stream The control string and data values are passed to the print function printf as parameters the control string as the first parameter and one parameter for each value to be printed In other words we supply the follow ing information to the print function 1 The format control string including any textual data to be inserted into the text stream 2 A set of zero or more data values to be formatted Figure 2 17 is a conceptional representation of the format control string and two conversion specifications Figure 2 17 a shows the format string and the data values as parameters for the print function Within the control string we have specified quantity Qty and total Tot as textual data and two conversion specifications d and f The first specification requires an integer type value the second requires a real type value We discuss the conversion specifications in detail in the following section Figure 2 17 b shows the formatting operation and the resulting text stream The first data value is a literal integer the second data value is the contents of a variable named tot This part of Figure 2 17 shows how the printf function expands t
39. cifications but only two values 2 printf d d n 44 55 66 44 55 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 62 Section 2 7 Input Output This example has two conversion specifications with three values In this case printf ignores the third value 3 float x 123 45 printf The data are d n x The data are 1079958732 This is a very common error in which the format specification integer does not match the data type real Input Formatting scanf The standard input formatting function in C is scanf scan formatting This function takes a text stream from the keyboard extracts and formats data from the stream according to a format control string and then stores the data in specified program variables For example the stream of 5 characters 2 3 4 2 and 2 are extracted as the real 234 2 Figure 2 19 shows the concept Data Source Text Stream Real 2 ig 14 og 7 Standard Input Program FIGURE 2 19 Formatting Text from an Input Stream The scanf function is the reverse of the printf function 1
40. ctured programming is the use of intelligent data names This means that the variable name itself should give the reader a good idea about what data it contains and maybe even an idea about how the data are used Although there are obvious advantages to keeping names short the advan tage is quickly lost if the names become so cryptic that they are unintelligible We have seen programmers struggle for hours to find a bug only to discover that the problem was the wrong variable was used The time saved keying short cryptic names is often lost ten or a hundredfold in debugging time We have formulated several guidelines to help you construct good intelli gent data names 1 The name should match the terminology of the user as closely as possible Let s suppose that you are writing a program to calculate the area of a rectangle Mathematicians often label the sides of a rectangle a and b but their real names are length and width Therefore your program should call the sides of the rectangle length and width These names are commonly used by anyone describing a rectangle 2 When necessary for readability and to separate similar variables from each other combine terms to form a variable name Suppose that you are working on a project to compute a payroll There are many different types of taxes Each of the different taxes should be clearly distinguished from the others by good data names Table 2 13 shows both good and bad names for th
41. ddress and so on This correspondence is very important It is also very important that the variable s type match the conversion specification type The C compiler does not verify that they match If they don t the input data will not be properly formatted when they are stored in the variable End of File and Errors In addition to whitespace and width specifications two other events stop the scanf function If the user signals that there is no more input by keying end of file EOF then scanf terminates the input process While there is no EOF on the keyboard it can be simulated in most systems For example Windows uses the lt ctrl z gt key combination to signal EOF Unix and Apple Macin tosh use lt ctrl d gt for EOF The C user s manual for your system should specify the key sequence for EOF Second if scanf encounters an invalid character when it is trying to con vert the input to the stored data type it stops The most common error is finding a nonnumeric character when it is trying to read a number The valid characters are leading plus or minus digits and one decimal point Any other combination including any alphabetic characters will cause an error Although it is possible to detect this error and ask the user to re input the data we will not be able to cover the conventions for this logic until Chapter 7 Until then be very careful when you enter data into your program Copyright 2007 by Thomson Course Techno
42. e Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 47 This program contains three different processes First it reads three numbers The code to read the numbers includes the printed instructions and a read scanf statement The second process adds the three numbers While this process consists of only a com ment and one statement we separate it from the read process This makes it easier for the reader to follow the program Finally we print the result Again the print process is separated from the calculate process by a blank line 2 6 Constants Constants are data values that cannot be changed during the execution of a program Like variables constants have a type In this section we discuss Boolean character integer real complex and string constants Constant Representation In this section we show how we use symbols to represent constants In the next section we show how we can code these constants in our program Boolean Constants A Boolean data type can take only two values Therefore we expect that we have only two
43. e manufactures and sellers Chapter 2 Introduction to the C Language 87 21 Which of the following identifiers are valid and which are invalid Explain your answer a num b num2 c 2dNum d 2d_num e num 2 22 Which of the following identifiers are valid and which are invalid Explain your answer a num 2 b num 2 c num 2 d _num2 e num 2 23 What is output from the following program fragment To show your out put draw a grid of at least 8 lines with at least 15 characters per line Local Declarations int x 10 char w Beau floatz Bg lake Statements printf nFirst nExample n joan ohena PEIGYelNiol Wir SHE Exe No Sen W printf Tees aley GoAie al b4 e 24 Find any errors in the following program This program does nothing int main return 0 25 Find any errors in the following program include stdio h int main void print Hello World return 0 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 88 Section 2 13 Practice Sets 26 Find any errors in the following program include lt s
44. ed by a new line n A binary stream consists of a sequence of data values such as inte ger real or complex using their memory representation In this chapter we briefly discuss only text streams A more detailed discussion of text streams is found in Chapter 7 Text Input Output and a detailed discussion of binary streams is found in Chapter 13 Binary Input Output A terminal can be associated only with a text stream because a keyboard can only send a stream of characters into a program and a monitor can only display a sequence of characters A file on the other hand can be associated with a text or binary stream We can store data in a file and later retrieve them as a sequence of characters text stream or as a sequence of data val ues binary streams Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 54 Section 2 7 Input Output In this chapter we assume that the source of data is the keyboard and the destination of data is the monitor In other words the terminal devices we use produce or consume text streams In C the keyboard is known as stan dard input
45. ed without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 33 Preprocessor directive to include lt stdio h gt lt _ include standard input output functions in the program int main void printf Hello World n Hello World return 0 main FIGURE 2 3 The Greeting Program Preprocessor Commands The preprocessor commands come at the beginning of the program All pre processor commands start with a pound sign this is just one of the rules of C known as its syntax Preprocessor commands can start in any column but they traditionally start in column 1 The preprocessor command tells the compiler to include the standard input output library file in the program You need this library file to print a message to the terminal Printing is one of the input output processes identi fied in this library The complete syntax for this command is shown below include lt stdio h gt The syntax of this command must be exact Since it is a preprocessor command it starts with the pound sign There can be no space between the pound sign and the keyword include Include means just what you would think it does It tells the preprocessor that you want the li
46. ee later variables are not initialized automatically When variables are defined they usually contain garbage meaningless values left over from a previous use so we need to initialize them or store data in them using run time statements before accessing their values Many compilers display a warning message when a variable is accessed before it is initialized When a variable is defined it is not initialized We must initialize any variable requiring prescribed data when the function starts One final point about initializing variables when they are defined Although the practice is convenient and saves you a line of code it also can lead to errors It is better therefore to initialize the variable with an assign ment statement at the proper place in the body of the code This may take another statement but the efficiency of the resulting program is exactly the same and you will make fewer errors in your code EXAMPLE 2 1 Print Sum At this point you might like to see what a more complex program looks like As you read Program 2 2 note the blank lines to separate different groups of code This is a good technique for making programs more readable You should use blank lines in your programs the same way you use them to sepa rate the paragraphs in a report Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced
47. eft justification because adding zeros after a number changes its value The sign flag defines the use or absence of a sign in a numeric value We can specify one of three formats default formatting print signed values or prefix positive values with a leading space Default formatting inserts a sign only when the value is negative Positive values are formatted without a sign When the flag is set to a plus signs are printed for both positive and neg ative values If the flag is a space then positive numbers are printed with a leading space and negative numbers with a minus sign Table 2 11 documents three of the more common flag options Flag Code Formatting Justification None se ee es Sign None positive value no sign negative value positive value negative value None positive value space negative value TABLE 2 11 Flag Formatting Options Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 59 Output Examples This section contains several output examples We show the prinif statement followed by wha
48. em Defined Value int Keyword TABLE 2 2 Examples of Valid and Invalid Names Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 38 Section 2 4 Types 2 4 Types A type defines a set of values and a set of operations that can be applied on those values For example a light switch can be compared to a computer type It has a set of two values on and off Only two operations can be applied to a light switch turn on and turn off The C language has defined a set of types that can be divided into four general categories void integral floating point and derived as shown in Figure 2 7 C Types In this chapter we concentrate only on the first three types The derived type will be discussed in future chapters FIGURE 2 7 Data Types Void Type The void type designated by the keyword void has no values and no opera tions Although having no values and operations might seem unusual the void type is a very useful data type For example it is used to designate that a func tion has no parameters as we saw in the main function It can also be used to
49. es that are too similar create confusion On the other hand a naming pattern makes it easier to recall the names This is especially true when user terminol ogy is being used Thus we see that the good names in Table 2 13 all start with fica 4 Abbreviations when used should clearly indicate the word being abbreviated Table 2 13 also contains several examples of good abbreviations Whenever possible use abbreviations created by the users They will often have a glossary of abbreviations and acronyms that they use Short words are usually not abbreviated If they are short in the first place they don t need to be made shorter 5 Avoid the use of generic names Generic names are programming or user jargon For example count and sum are both generic names They tell you their purpose but don t give you any clue as to the type of data they are associated with Better names would be emplyCnt and ficaSum Programmers are especially fond of using generic names but they tend to make the program confus ing Several of the poor names in Table 2 13 are generic 6 Use memory constants or defined constants rather than literals for values that are hard to read or that might change from system to system Some constants are nearly impossible to read We pointed out the space earlier If you need a space often create a defined constant for it Table 2 14 contains several examples of constants that are better when coded as defined constants
50. ether as are all the uppercase letters and the digits Many of the special characters such as the shift char acters on the top row of the keyboard are grouped together but some are found spread throughout the alphabet What makes the letter a different from the letter x In English it is the visual formation of the graphic associated with the letter In the computer it is the underlying value of the bit configuration for the letter The letter a is binary 0110 0001 The letter x is 0111 1000 The decimal values of these two binary numbers are 97 and 120 respectively To support non English languages and languages that don t use the Roman alphabet the C99 standard created the wide character type Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 40 Section 2 4 Types wchar_t Without going in to all of the complexities C supports two inter national standards one for four type characters and one for two byte charac ters Both of these standards support the traditional characters found in ASCII that is all extensions occur above the last ASCII character The origi nal ASC
51. g point of view We will dis cuss the concepts of program documentation data naming and data hiding Program Documentation There are two levels of program documentation The first is the general docu mentation at the start of the program The second level is found within each function General Documentation Program 2 11 shows what we recommend for program documentation Each program should start with a general description of the program Following the general description is the name of the author and the date the program was written Following the date is the program s change history which documents the reason and authority for all changes For a production program whose use spans several years the change history can become extensive PROGRAM 2 11 Sample of General Program Documentation A sample of program documentation Each program starts with a general description of the program Often this description can be taken from the requirements specification given to the programmer Written by original author Date Date first released to production Change History lt date gt Included in this documentation is a short description of each change oCoMWO MON HD U FWD Module Documentation Whenever necessary we include a brief comment for blocks of code A block of code is much like a paragraph in a report It contains one thought that is one set of statements that accomplish a specific task Blocks
52. have explained everything in this program but the preprocessor commands They are special instructions to the preprocessor that tell it how to prepare the program for compilation One of the most important of the preprocessor commands and one that is used in virtually all programs is include The include command tells the preprocessor that we need information from selected libraries known as header files In today s complex programming environments it is almost impossible to write even the smallest of programs without at least one library function In your first program you will use one include command to tell C that you need the input output library to write data to the monitor a Preprocessor Directives Global Declarations int main void Local Declarations Statements main Other functions as required FIGURE 2 2 Structure of a C Program Your First C Program Your first C program will be very simple see Figure 2 3 It will have only one preprocessor command no global declarations and no local definitions Its purpose will be simply to print a greeting to the user Therefore its statement section will have only two statements one that prints a greeting and one that stops the program Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduc
53. he control stream and inserts the data values and text characters Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 56 Section 2 7 Input Output a Basic Concept Format Control String 23 48 53 Data Values printf E SOCOONEENCCCONGOCECEA lt b Implementation FIGURE 2 17 Output Stream Formatting Example Format Control String Text The control string may also contain text to be printed such as instructions to the user captions or other identifiers and other text intended to make the output more readable In fact as we have already seen the format string may contain nothing but text in which case the text will be printed exactly as shown We used this concept when we wrote the greeting program In addi tion we can also print control characters such as tabs t newlines n and alerts a by including them in the format string Tabs are used to for mat the output into columns Newlines terminate the current line and con tinue formatting on the next line Alerts sound an audio signal to alert usually
54. he input character For example to read three characters we should code the following format string Note the spaces before each conversion specification scanf u ecir su ACI mes Cay mec Slr Figure 2 20 demonstrates the input format string concept with a control string having two fields d and f The first one defines that a character will be inserted here the second defines that a real will be inserted there We will discuss these place holders or format specifiers later in the chapter Format Control String Like the control string for printf the control string for scanf is enclosed in a set of quotation marks and contains one or more conversion specifications that describe the data types and indicate any special formatting rules and or characters Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 64 Section 2 7 Input Output a Basic Concept Format Control String Text Stream Data Values Al RAN ia price code Discarded b Implementation FIGURE 2 20 Input Stream Formatting Example Conversion Specificatio
55. his is a whole line comment a 5 This is a partial line comment FIGURE 2 5 Examples of Line Comments Although they can appear anywhere comments cannot be nested In other words we cannot have comments inside comments Once the compiler sees an opening block comment token it ignores everything it sees until it finds the closing token Therefore the opening token of the nested comment is not recognized and the ending token that matches the first opening token is left standing on its own This error is shown in Figure 2 6 FIGURE 2 6 Nested Block Comments Are Invalid The Greeting Program Program 2 1 shows the greeting program just as we would write it We have included some comments at the beginning that explain what the program is going to do Each program we write begins with documentation explaining the purpose of the program We have also shown comments to identify the declaration and statement sections of our program The numbers on the left in Program 2 1 and the other programs in the text are for discussion refer ence They are not part of the program Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademark
56. hts reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 43 Variable Declaration Each variable in your program must be declared and defined In C a declara tion is used to name an object such as a variable Definitions are used to create the object With one exception a variable is declared and defined at the same time The exception which we will see later declares them first and then defines them at a later time For variables definition assumes that the declaration has been done or is being done at the same time While this dis tinction is somewhat of an oversimplification it works in most situations We won t worry about the exception at this time When we create variables the declaration gives them a symbolic name and the definition reserves memory for them Once defined variables are used to hold the data that are required by the program for its operation Gen erally speaking where the variable is located in memory is not a program mer s concern it is a concern only of the compiler From our perspective all we are concerned with is being able to access the data through their symbolic n
57. ious as to why the underscore is included among the possible characters that can be used for an identifier It is there so that we can separate different parts of an identifier To make identifiers descriptive we often combine two or more words When the names contain multiple words the underscore makes it easier to read the name An identifier must start with a letter or underscore it may not have a space or a hyphen Another way to separate the words in a name is to capitalize the first let ter in each word The traditional method of separation in C uses the under score A growing group of programmers however prefer to capitalize the first letter of each word Table 2 2 contains examples of valid and invalid names C is a case sensitive language Two more comments about identifiers Note that some of the identifiers in Table 2 2 are capitalized Typically capitalized names are reserved for pre processor defined names The second comment is that C is case sensitive This means that even though two identifiers are spelled the same if the case of each corresponding letter doesn t match C thinks of them as different names Under this rule num Num and NUM are three different identifiers Valid Names Invalid Name a Valid but poor style sum is illegal student_name 2names First char digit _aSystemName sum salary Contains hyphen Bool Boolean System id stdnt Nmbr Contains spaces INT_MIN Syst
58. is programming situa tion Most of the poor names are either too abbreviated to be meaningful such as ftr or are generic names such as rate that could apply to many different pieces of data Good Names Poor Names ficaTaxRate fica_tax_rate rate ftr frate fica ficaWitholding fica_witholding fwh ficaw wh ficaWthldng fica_wthldng fewthldng wthldng TABLE 2 13 Examples of Good and Poor Data Names Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 79 Note the two different concepts for separating the words in a vari able s name demonstrated in Table 2 13 In the first example we capital ized the first letter of each word In the second example we separated the words with an underscore Both are good techniques for making a com pound name readable If you use capitalization keep in mind that C is case sensitive so you must be careful to use the same cases for the name each time you use it 3 Do not create variable names that are different by only one or two letters especially if the differences are at the end of the word Nam
59. iting from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 60 Section 2 7 Input Output Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 10 11 printf The number is 6d 23 The number is 23 AKRRAKRARAKRARARAARAKRAABRARAN If you count the spaces carefully you will note that five spaces follow the word is The first space comes from the space after is and before the 3 in the format string The other four come from the width in the conversion specification printf The tax is 6 2f this year 233 12 Thestax isi 2337 025 this vyear In this example the width is six and the precision two Since the number of digits printed totals five three for the integral portion and two for the decimal portion and the decimal point takes one print position the full width is filled with data The only spaces are the spaces before and after the conversion code in the format string print The tax is 8 2 this
60. logy All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 66 Section 2 7 Input Output Input Formatting Summary Table 2 12 summarizes the rules for using scanf The conversion operation processes until a End of file is reached b The maximum number of characters has been processed c A whitespace character is found after a digit in a numeric specification d An error is detected There must be a conversion specification for each variable to be read There must be a variable address of the proper type for each conversion specification Any character in the format string other than whitespace or a conver sion specification must be exactly matched by the user during input If the input stream does not match the character specified an error is sig naled and scanf stops It is a fatal error to end the format string with a whitespace character Your program will not run correctly if you do TABLE 2 12 scanf Rules Input Examples This section contains several examples We list the data that will be input first This allows you to cover up the function and try to formulate your own scanf statement 1
61. maginary constants we need to talk about complex constants that are widely used in engineering Complex constants are coded as two parts the real part and the imagi nary part separated by a plus sign The real part is coded using the real for mat rules The imaginary part is coded as a real number times the imaginary constant _Complex_I If the complex library complex h is included the imaginary constant can be abbreviated as I Examples are shown in Table 2 9 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 50 Section 2 6 Constants Representation Value Type 12 8 IAAL 12 3 14 4 1 2 double complex JAF 16F 14 16 1 2 float complex 1 4736L 4 56756L 1 1 4736 4 56756 1 2 long double complex TABLE 2 9 Examples of Complex Constants The default form for complex constants is double If we want the result ing data type to be float or long double we must use a code to specify the desired data type As you might anticipate f and F are used for float and 1 and L are used for long double Again do not use the lowercase fo
62. mission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 58 Section 2 7 Input Output of 7 2 is designed to print a maximum value of 9999 99 Some examples of width specifications and precision are shown below S2hd short integer 2 print positions 34d integer 4 print positions 81d long int 8 not 81 positions Sie 2E float 7 print positions nnnn dd 310 3Lf long double 10 positions nnnnnn ddd The flag modifier is used for four print modifications justification pad ding sign and numeric conversion variants The first three are discussed here the conversion variants are discussed in Chapter 7 Justification controls the placement of a value when it is shorter than the specified width Justification can be left or right If there is no flag and the defined width is larger than required the value is right justified The default is right justification To left justify a value the flag is set to minus Padding defines the character that fills the unused space when the value is smaller than the print width It can be a space the default or zero If there is no flag defined for padding the unused width is filled with spaces if the flag is 0 the unused width is filled with zeroes Note that the zero flag is ignored if it is used with l
63. n To format data from the input stream we use a conversion specification that contains a start token a conversion code and up to three optional modifiers as shown in Figure 2 21 Only the field specification token and the conversion code are required Maximum A FIGURE 2 21 Conversion Specification There are only three differences between the conversion codes for input formatting and output formatting First there is no precision in an input con version specification It is an error to include a precision if scanf finds a pre cision it stops processing and the input stream is in the error state There is only one flag for input formatting the assignment suppression flag More commonly associated with text files see Chapter 7 the assign ment suppression flag tells scanf that the next input field is to be read but not stored It is discarded The following scanf statement reads an integer a char acter and a floating point number from the input stream The character is read and discarded The other fields are read formatted and stored Note that there is no matching address parameter for the data to be discarded scanf Use ttm sti Gk Ey Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names ha
64. n zero 35 printf ASCII for char 8 is d n eight 36 printf ASCII for char n is d n NL 37 printf ASCII for char t is d n HT 38 printf ASCII for char v is d n VT 39 printf ASCII for char is d n SP 40 printf ASCII for char a is d n BEL 41 printf ASCII for char is d n dblQuote 42 printf ASCII for char is d n backSlash 43 printf ASCII for char is d n oneQuote 44 continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 71 PROGRAM 2 6 Print Value of Selected Characters continued 45 return 0 46 main Results ASCII for character A is 65 ASCII for character a is 97 ASCII for character B is 66 ASCII for character b is 98 ASCII for character Z is 90 ASCII for character z is 122 ASCII for character 0 is 48 ASCIZ for character 8 is 56 ASCII for character n is 10 ASCII form character Nt is 9 ASCII for character v is 11 ASCE for character u is 32 ASCIT fon character Nat is 7
65. nt tokens is ignored by the compiler The tokens can start in any column and they do not have to be on the same line The only require ment is that the opening token must precede the closing token Figure 2 4 shows two examples of block comments This is a block comment that covers two lines ari It is a very common style to put the opening token on a line by itself followed by the documentation and then the closing token on a separate line Some programmers also like to put asterisks at the beginning of each line to clearly mark the comment ad FIGURE 2 4 Examples of Block Comments Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 35 Line Comment The second format the line comment uses two slashes to identify a comment This format does not require an end of comment token the end of the line automatically ends the comment Programmers generally use this format for short comments The line comment token can start anywhere on the line Figure 2 5 contains two examples of line comments T
66. numbers forward T5 35 72 Your numbers reversed 72 35 T5 42 Write a program that reads 10 integers and prints the first and the last on one line the second and the ninth on the next line the third and the sev enth on the next line and so forth Sample input and the results are shown below Please enter 10 numbers O S A ya A GS E Sy e e Your numbers are TOMO SI IS A sha tS 24 65 43 Write a program that reads nine integers and prints them three in a line separated by commas as shown below Input VOWS IS 2 573924656987 1 8 Output UO Sil 2 Uap Bay 95 Op Wi alts Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers
67. of code in our program are separated by blank program lines just as we skip blank lines between paragraphs in reports If the block of code is difficult or if the logic is especially significant then we give the reader a short one or two line description of the block s purpose and or operation We will provide many examples of this type of doc umentation throughout the text Sometimes a textbook suggests that each variable in a program be docu mented We disagree with this approach First the proper location for vari able documentation is in a data dictionary A data dictionary is a system Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 78 Section 2 9 Software Engineering documentation tool that contains standard names descriptions and other information about data used in a system Second good data names eliminate the need for variable comments In fact if you think you need to document the purpose of a variable check your variable name You will usually find that improving the name eliminates the need for the comment Data Names Another principle of good stru
68. of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 51 It is important to understand the difference between the null character see Table 2 6 and an empty string The null character represents no value As a character it is 8 zero bits An empty string on the other hand is a string containing nothing Figure 2 14 shows the difference between these two con stant types NOT Null character un Empty string FIGURE 2 14 Null Characters and Null Strings At this point this is all you need to know about strings We talk more about them and how they are stored in the computer when we study strings in Chapter 11 Use single quotes for character constants Use double quotes for string constants Coding Constants In this section we discuss three different ways we code constants in our pro grams literal constants defined constants and memory constants Literal Constants A literal is an unnamed constant used to specify data If we know that the data cannot be changed then we can simply code the data value itself in a statement Literals are coded as part of a statement using the constant formats described in the previous section For example the literal 5 is used in the fol lowing statement a bd Defined Constants Another way to design
69. or on the vertical axis y In C we use complex number and a predefined library function to print the real and imaginary values We can also find the length of the vector which is the abso lute value of the complex number and the angle of the vector which is the argument of the vector These four attributes are shown in Figure 2 23 Imaginary FIGURE 2 23 Complex Number Attributes As the figure shows the absolute value of the complex a b I can be found as a b 2 The argument can be found as arctan b a The conjugate of a complex number is another complex number defined as a b I Program 2 9 shows how we print the different attributes of a complex number using the predefined functions creal cimag cabs and carg PROGRAM 2 9 Print Complex Number Attributes Print attributes of a complex number Written by Date include lt stdio h gt include lt math h gt include lt complex h gt Oo WAND UW FWD int main void continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 7
70. ourse Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 70 Section 2 8 Programming Examples PROGRAM 2 6 Print Value of Selected Characters 1 Display the decimal value of selected characters 2 written by 3 Date 4 5 include lt stdio h gt 6 7 int main void 8 9 Local Declarations 10 char A A 11 char a a 12 char B B 13 char b m 14 char Zed Z 15 char zed Z s 16 char zero 0 E7 char eight 8 18 char NL n newline 19 char HT t horizontal tab 20 char VT v vertical tab 21 char SP Sak c3 blank or space 22 char BEL a alert bell 23 char dblQuote double quote 24 char backSlash backslash itself 25 char oneQuote single quote itself 26 27 Statements 28 printf ASCII for char A is d n A 29 printf ASCII for char a is d n a 30 printf ASCII for char B is d n B 31 printf ASCII for char b is d n b 32 printf ASCII for char Z is d n Zed 33 printf ASCII for char z is d n zed 34 printf ASCII for char 0 is d
71. pany names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 76 Section 2 8 Programming Examples PROGRAM 2 10 Complex Number Arithmetic continued 18 19 Statements 20 sum x y 21 dif x y 22 mul x y 23 div x y 24 25 printf sf f sf f n creal sum cimag sum 26 cabs sum carg sum 27 printf sf sf sf f n creal dif cimag dif 28 cabs dif carg dif 29 printf sf gf sf f n creal mul cimag mul 30 cabs mul carg mul 31 printf sf gf Sf f n creal div cimag div 32 cabs div carg div 33 return 0 34 main Results 6 000000 0 000000 6 000000 0 000000 0 000000 8 000000 8 000000 1 570796 25 000000 0 000000 25 000000 0 000000 0 280000 0 960000 1 000000 1 854590 Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 77 2 9 Software Engineering Although this chapter introduces only a few programming concepts there is still much to be said from a software engineerin
72. part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 53 PROGRAM 2 3 Memory Constants continued 9 int main void 10 11 Local Declarations 12 const double cPi PI 13 14 Statements 15 printf Defined constant PI f n PI 16 printf Memory constant cPi f n PI 17 printf Literal constant Sf n 3 1415926536 18 return 0 19 main Results Defined constant PI 3 141593 Memory constant cPi 3 141593 Literal constant 3 141593 2 7 Input Output Although our programs have implicitly shown how to print messages we have not formally discussed how we use C facilities to input and output data We devote two chapters Chapters 7 and 13 to fully explain the C input output facilities and how to use them In this section we describe simple input and output formatting Streams In C data is input to and output from a stream A stream is a source of or destination for data It is associated with a physical device such as a termi nal or with a file stored in auxiliary memory C uses two forms of streams text and binary A text stream consists of a sequence of characters divided into lines with each line terminat
73. r long dou ble it is too easily confused with the number 1 The two components of a complex constant must be of the same precision that is if the real part is type double then the imaginary time must also be type double Table 2 9 shows several examples of complex constants Note that we use the abbreviated form for the imaginary part String Constants A string constant is a sequence of zero or more characters enclosed in double quotes You used a string in your first program without even knowing that it was a string Look at Program 2 1 to see if you can identify the string Listed in Figure 2 13 are several strings including the one from Program 2 1 The first example an empty string is simply two double quotes in succes sion The second example a string containing only the letter h differs from a character constant in that it is enclosed in double quotes When we study strings we will see that there is also a big difference in how h is stored in memory as a character and as a string The last example is a string that uses wide characters on A null string hh Hello World n HOW ARE YOU Good Morning L This string contains wide characters FIGURE 2 13 Some Strings Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some
74. rintable ASCII character can be used in an identifier a True b False The C standard function that receives data from the keyboard is printf Qo a True b False 4 Which of the following statements about the structure of a C program is false a AC program starts with a global declaration section b Declaration sections contain instructions to the computer c Every program must have at least one function d One and only one function may be named main e Within each function there is a local declaration section VW Which of the following statements about block comments is false a Comments are internal documentation for programmers b Comments are used by the preprocessor to help format the program c Comments begin with a token d Comments cannot be nested e Comments end with a token P Which of the following identifiers is not valid a _option b amount c sales_amount d salesAmount e salesAmount S Which of the following is not a data type a char b float c int d logical e void Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manuf
75. s documented and popularized in a 1978 book by Brian W Kernighan and Dennis Ritchie In 1983 the American National Standards Institute ANSI began the definition of a standard for C It was approved in December 1989 In 1990 the International Standards Organization ISO adopted the ANSI standard This version of C is known as C89 In 1995 minor changes were made to the standard This version is known as C95 A much more significant update was made in 1999 The changes incorporated into the standard now known as C99 are summarized in the following list Extensions to the character type to support non English characters A Boolean type Extensions to the integer type Inclusion of type definitions in the for statement Addition of imaginary and complex types n wi BW N e Incorporation of the C style line comment We use the Standard C in this book 2 2 C Programs It s time to write your first C program This section will take you through all the basic parts of a C program so that you will be able to write it Structure of a C Program Every C program is made of one or more preprocessor commands a global dec laration section and one or more functions The global declaration section comes at the beginning of the program We will talk more about it later but the basic idea of global declarations is that they are visible to all parts of the program The work of the program is carried out by its functions
76. s and sellers Chapter 2 Introduction to the C Language 83 1 To make a program more readable use comments A comment is a sequence of characters ignored by the compiler C uses two types of com ments block and line A block comment starts with the token and ends with the token A line comment starts with the token the rest of the line is ignored T Identifiers are used in a language to name objects T C types include void integral floating point and derived T A void type is used when C needs to define a lack of data T An integral type in C is further divided into Boolean character and integer E A Boolean data type takes only two values true and false It is desig nated by the keyword bool E A character data type uses values from the standard alphabet of the lan guage such as ASCII or Unicode There are two character type sizes char and w_char E An integer data type is a number without a fraction C uses four differ ent integer sizes short int int long int and long long int T The floating point type is further divided into real imaginary and complex E A real number is a number with a fraction It has three sizes float double and long double E The imaginary type represents the imaginary part of a complex number It has three sizes float imaginary double imaginary and long double imaginary The complex type contains a real and an imaginary part C uses three complex sizes floa
77. s of their respective manufactures and sellers 36 Section 2 3 Identifiers PROGRAM 2 1 The Greeting Program 1 The greeting program This program demonstrates 2 some of the components of a simple C program 3 Written by your name here 4 Date date program written 5 6 include lt stdio h gt 7 8 int main void 2 ek 10 Local Declarations 11 12 Statements 13 14 printf Hello World n 15 16 return 0 17 FP _ main 2 3 Identifiers One feature present in all computer languages is the identifier Identifiers allow us to name data and other objects in the program Each identified object in the computer is stored at a unique address If we didn t have identi fiers that we could use to symbolically represent data locations we would have to know and use object s addresses Instead we simply give data identifi ers and let the compiler keep track of where they are physically located Different programming languages use different syntactical rules to form identifiers In C the rules for identifiers are very simple The only valid name symbols are the capital letters A through Z the lowercase letters a through z the digits 0 through 9 and the underscore The first character of the identi fier cannot be a digit Typically application programs do not use the underscore for the first character either because many of the identifiers in the C system libraries start with
78. s the signed integer of the same size Table 2 3 contains typical values for the integer types Recognize however that the actual sizes are dependent on the physical hardware 3 For a complete discussion see Appendix D Numbering Systems Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 41 Type Byte Minimum Value Maximum Value Size short int 32 768 S267 int 2 147 483 648 2 147 483 647 2 147 483 648 2 147 483 647 long long int 9 223 372 036 854 775 807 9 223 372 036 854 775 806 TABLE 2 3 Typical Integer Sizes and Values for Signed Integers To provide flexibility across different hardware platforms C has a library limits h that contains size information about integers For example the mini mum integer value for the computer is defined as INT_MIN and the maxi mum value is defined as INT MAX See Appendix E Integer and Float Libraries for a complete list of these named values Floating Point Types The C standard recognizes three floating point types real imaginary and complex Like the limi
79. sed in parentheses For your simple program the parameter list simply contains what you want dis played enclosed in two double quote marks The n at the end of the message tells the computer to advance to the next line in the output The last statement in your program return 0 terminates the program and returns control to the operating system One last thing The function main starts with an open brace and terminates with a close brace Comments Although it is reasonable to expect that a good programmer should be able to read code sometimes the meaning of a section of code is not entirely clear This is especially true in C Thus it is helpful if the person who writes the code places some comments in the code to help the reader Such comments are merely internal program documentation The compiler ignores these comments when it translates the program into executable code To identify a comment C uses two different formats block comments and line comments Block Comment A block comment is used when the comment will span several lines We call this comment format block comment It uses opening and closing comment tokens A token is one or more symbols understood by the compiler that help it interpret code Each comment token is made of two characters that taken together form the token there can be no space between them The opening token is and the closing token is Everything between the opening and closing comme
80. see Appendix G Preprocessor Commands Memory Constants The third way to use a constant is with memory constants Memory constants use a C type qualifier const to indicate that the data cannot be changed Its format is const type identifier value We have seen how to define a variable which does nothing more than give a type and size to a named object in memory Now let us assume that we want to fix the contents of this memory location so that they cannot be changed This is the same concept as a literal only now we give it a name The following code creates a memory constant cPi To help us remember that it is a constant we preface the identifier name with c const float cPi 3 14159 Three points merit discussion 1 The type qualifier comes first 2 Then there must be an initializer If we didn t have an initializer then our named constant would be whatever happened to be in memory at cPi s location when our program started 3 Finally since we have said that cPi is a con stant we cannot change it Program 2 3 demonstrates the three different ways to code pi as a constant PROGRAM 2 3 Memory Constants This program demonstrates three ways to use constants Written by Date include lt stdio h gt define PI 3 1415926536 ANA UF WDNY FE continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No
81. sun initialized or is only sum initialized int count sum 0 The answer is that the initializer applies only to the variable defined immediately before it Therefore only sum is initialized If you wanted both variables initialized you would have to provide two initializers int count 0 sum 0 4 The assignment operator is the equal sign Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 45 Again to avoid confusion and error we prefer using only one variable definition to a line The preferred code in this case would be ll i int count int sum se Ne ll oO Figure 2 12 repeats Figure 2 11 initializing the values in each of the variables char code b B code int i 14 ia i long long natl_debt 1000000000000 1000000000000 nat1_debt float payRate 14 25 14 25 payRate double pi 3 1415926536 Beno O gt eiom pi Program Memory FIGURE 2 12 Variable Initialization It is important to remember that with a few exceptions that we will s
82. t complex double complex and long double complex T A constant is data whose value cannot be changed T Constants can be coded in three different ways as literals as define com mands and as memory constants T Variables are named areas of memory used to hold data T Variables must be declared and defined before being used in C T To input data through the keyboard and to output data through the moni tor use the standard formatted input output functions I scanf is a standard input function for inputting formatted data through the keyboard I printf is a standard output function for outputting formatted data to the monitor LI As necessary programs should contain comments that provide the reader with in line documentation for blocks of code _1 Programs that use intelligent names are easier to read and understand Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 84 Section 2 13 Practice Sets 2 13 Practice Sets Review Questions 1 The purpose of a header file such as stdio h is to store a program s source code a True b False Any valid p
83. t of 1 V 1 The imaginary type like the real type can be of three different sizes float imaginary double imaginary and long double imaginary Most C implementations do not support the imaginary type yet and the functions to handle them are not part of the standard We mention them here because the imaginary type is one of the components of the complex type Complex C defines a complex type which is implemented by most compilers A com plex number is a combination of a real and an imaginary number The com plex type like the real type can be of three different sizes float complex double complex and long long complex The size needs to be the same in both the real and the imaginary part We provide two program examples that use complex numbers at the end of this chapter Type Summary A summary of the four standard data types is shown in Table 2 4 Category Type C Implementation short int int long int long long int Floating Point Rel float double long double Imaginary float imaginary double imaginary long double imaginary Complex float complex double complex long double complex TABLE 2 4 Type Summary 2 5 Variables Variables are named memory locations that have a type such as integer or character which is inherited from their type The type determines the values that a variable may contain the operations that may be used with its values Copyright 2007 by Thomson Course Technology All rig
84. t would be printed Cover up the solution and try to predict the results l print d c f 23 z 4 1 23z4 100000 Note that because there are no spaces between the conversion speci fications the data are formatted without spaces between the values 2 print sd se f 23 t21 4 1 23 z 4 100000 This is a repeat of Output Example 1 with spaces between the con version specifications Saint numl 23 char zee o float num2 4 1 printf d c f numl zee num2 23 z 4 100000 Again the same example this time using variables 4 printf d t c t 5 1f n 23 Z 14 2 pringt td ec tspalf n wor A 53 6 printf Sd t c t 5 1f n 1754 F 122 0 printf Sd t c t 5 1f n 3 P 0 1 23 Z 14 2 107 A 53 6 1754 F LAA 50 3 P ori In addition to the conversion specifications note the tab character t between the first and second and second and third conversion spec ifications Since the data are to be printed in separate lines each format string ends with a newline n 5 printf The number dis my favorite number 23 The number23is my favorite number Since there are no spaces before and after the format code d the number 23 is run together with the text before and after Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in wr
85. tdio gt int main void printf We are to learn correct printf C language here return 0 main 27 Find any errors in the following program This is a program with some errors in it to be corrected int main void Local Declarations integer a floating point b character Cy Statements printf The end of the program return 0 y main 28 Find any errors in the following program This is another program with some errors in it to be corrected int main void Local Declarations a int b float double cr di char Statements printf The end of the program return 0 main 29 Find any errors in the following program This is the last program to be corrected in these exercises continued Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 89 int main void Local Declarations aint ley el Bg Gl elocties aay eye doubles float Statements printf The end of return 0 Ly main the program Problems 30 31
86. tity on hand the current quantity on order and the price of the item printed to two decimal points All data should be aligned in columns with captions indicating the type of data in each column The report should be closed with an End of Report message PROGRAM 2 8 A Sample Inventory Report AANA UM FPF WN FE oO 10 1a 12 13 14 15 16 17 18 1g 20 21 22 23 24 25 26 27 28 29 30 31 This program will print four lines of inventory data on an inventory report to give the user an idea of what a new report will look like Since this is not a real report no input is required The data are all specified as constants Written by Date si include lt stdio h gt int main void Statements Print captions printf tPart Number tQty On Hand printf tOty On Order tPrice n Print data printf t S06d t tS7d t tS7d t t 37 2 n 31235 22 086 45 62 print t S06d t tS7d t tS7d t t 37 2 n 321 55 24122 print t S06d t tS7d t tS7d t t 37 2f n 28764 0 24 75 print t S06d t tS7d t tS7d t t 37 2 n 3232 12 0 10 91 Print end message printf n tEnd of Report n return 0 main Program 2 8 Analysis There are a few things about Program 2 8 that you should note First it is fully docu mented Professional programmers often ignore documentation on one time only programs thinking they will throw them away only to find
87. ts library for integer values there is a standard library float h for the floating point values see Appendix E Integer and Float Libraries Unlike the integral type real type values are always signed Real The real type holds values that consist of an integral and a fractional part such as 43 32 The C language supports three different sizes of real types float double and long double As was the case for the integer type real num bers are defined so that they can be organized from smallest to largest The relationship among the real types is seen in Figure 2 10 p float double long double FIGURE 2 10 Floating point Types Regardless of machine size C requires that the following relationship must be true sizeof float lt sizeof double lt sizeof long double Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 42 Section 2 5 Variables Imaginary Type C defines an imaginary type An imaginary number is used extensively in mathematics and engineering An imaginary number is a real number multi plied by the square roo
88. ublication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 86 Section 2 13 Practice Sets Exercises 14 15 16 17 18 19 20 Which of the following is not a character constant in C a C b bb Ce MGT d e Which of the following is not an integer constant in C 320 45 31 80 1456 2 456 gp Rose Which of the following is not a floating point constant in C 45 6 14 05 tat pi 40 gp Ro re What is the type of each of the following constants 15 14 24 b 1 il 6 n Which of the following is not a valid identifier in C A3 4A af IF tax rate gp Ro re Po re What is the type of each of the following constants ngh 3 3 14159 2 oy Del choos What is the type of each of the following constants Hello 15L 8 5L BoE a go Ro re Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respectiv
89. use problems A better solution would be to prompt the user separately for the month the day and the year Common Input Errors Each of the following examples has at least one error Try to find it before you look at the solution Your results may vary depending on your compiler and hardware l int a 0 scanf d a printf d n a 234 Input 0 Output This example has no address token on the variable sa If the pro gram runs at all the data are read into an unidentified area in memory What is printed is the original contents of the variable in this case 0 2 float a 2 1 scanf 5 2f amp a printf 5 2f a 74 35 Input 2 10 Output This example has no precision in the input conversion specification When scanf finds a precision it stops processing and returns to the func tion that called it The input variable is unchanged 3 int a int be scanf Sdsd d amp a amp b printf Sd d n a b Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 68 Section 2 8 Programming Examples ol a Oo input 5 10 output
90. ve been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 65 The third difference is the width specification with input formatting it is a maximum not a minimum width The width modifier specifies the maxi mum number of characters that are to be read for one format code When a width specification is included therefore scanf reads until the maximum number of characters have been processed or until scanf finds a whitespace character If scanf finds a whitespace character before the maximum is reached it stops Input Parameters For every conversion specification there must be a matching variable in the address list The address list contains the address of the matching variable How do we specify an address It s quite simple Addresses are indicated by prefixing the variable name with an ampersand amp In C the ampersand is known as the address operator Using the address operator if the variable name is price then the address is amp price Forgetting the ampersand is one of the most common errors for beginning C programmers so you will have to concentrate on it when you use the scanf function scanf requires variable addresses in the address list Remember that the first conversion specification matches the first vari able address the second conversion specification matches the second variable a
91. we recommend that you always use uppercase to avoid confusion especially with the lowercase letter 1 which often looks like the number 1 Table 2 7 shows several examples of integer constants The default types are typical for a personal computer Copyright 2007 by Thomson Course Technology All rights reserved This publication is protected by federal copyright law No part of this publication may be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers Chapter 2 Introduction to the C Language 49 Representation 123 123 int 378 378 int 232271 32 271 long int 76542LU 76 542 unsigned long int 127898451 12 789 845 long long int TABLE 2 7 Examples of Integer Constants Real Constants The default form for real constants is double If we want the resulting data type to be float or long double we must use a code to specify the desired data type As you might anticipate and F are used for float and 1 and L are used for long double Again do not use the lowercase for long double it is too eas ily confused with the number 1 Table 2 8 shows several examples of real constants Representation Value Type ES o ooe O I TABLE 2 8 Examples of Real Constants Complex Constants Although we do not discuss the i
92. without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 46 Section 2 5 Variables PROGRAM 2 2 Print Sum of Three Numbers 1 This program calculates and prints the sum of 2 three numbers input by the user at the keyboard 3 Written by 4 Date 5 6 include lt stdio h gt 7 8 int main void 9 10 Local Declarations 11 Int a 12 int b 13 intag 14 int sum 15 16 Statements E7 printf nWelcome This program adds n 18 printf three numbers Enter three numbers n 19 printf in the form nnn nnn nnn lt return gt n 20 scanf d d d amp a amp b amp C 21 22 Numbers are now in a b and c Add them 23 sum a b cC 24 25 printf The total is d n n sum 26 27 printf Thank you Have a good day n 28 return 0 29 main Results Welcome This program adds three numbers Enter three numbers in the form nnn nnn nnn lt return gt Hil 2A 3g The total is 66 Thank you Have a good day Program 2 2 Analysis Study the style of this program carefully First note how we start with a welcome message that tells the user exactly what needs to be entered Similarly at the end of the program we print an ending message It is a good style to print a start and end messag
93. y be reproduced without prior permission in writing from Course Technology Some of the product names and company names have been used for identification purposes only and may be trademarks or registered trademarks of their respective manufactures and sellers 35 Write a program that uses defined constants for the vowels in the alpha bet and memory constants for the even decimal digits 0 2 4 6 8 It then prints the following three lines using literal constants for the odd digits a e l UA A G G WS Bo y 36 Write a program that defines five integer variables and initializes them to 1 10 100 1000 and 10000 It then prints them on a single line sepa rated by space characters using the decimal conversion code d and on the next line with the float conversion code Note the differences between the results How do you explain them 37 Write a program that prompts the user to enter a quantity and a cost The values are to be read into an integer named quantity and a float named unitPrice Define the variables and use only one statement to read the values After reading the values skip one line and print each value with an appropriate name ona separate line 38 Write a program that prompts the user to enter an integer and then prints the integer first as a character then as a decimal and finally as a float Use separate print statements A sample run is shown below The number as a character K The number

Chapter 2 Introduction to the C Language

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