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1. BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange James Tam Purpose Of Named Constants 3 One change in the BIRTH_RATE 0 8 initialization of the MORTALITY_RATE 0 1257 constant changes every populationChange 0 reference to that currentPopulation 1000000 constant populationChange BIRTH_RAT currentPopulation if populationChange gt 0 print Increase print Birth rate BIRTH_RATE Morta fy ratg MORTALITY_RATE Population change populationChange elif populationChange lt 0 print Decrease print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange else print No change print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange James Tam Purpose Of Named Constants 4 One change in the BIRTH_RATE 0 1758 initialization of the MORTALITY_RATE 0 01 constant changes every populationChange 0 reference to that currentPopulation 1000000 constant populationChange BIRTH_RATE MORTALITY_RATE cugrentPopulation if populationChange gt 0 print Increase print Birth rate BIRTH_RATE Mortality rate MORTALI ATE Population change populationChange elif populationChange lt 0 print Decrease print Birth rate BIRTH_RATE Mortality rate MORTALITY_JRATE Population change populationChange else print No c2. 9 2 James Tam Augmented Assignment Operators Shortcuts Operator Long example Augmented Shortcut num num 1 num 1 num num 1 num 1 num num 2 num 2 num num 2 num 2 num num 2 num 2 num num 2 num 2 James Tam Order Of Operation First level of precedence top to bottom Second level of precedence If there are multiple operations that are on the same level then precedence goes from left to right Brackets inner before outer Exponent Multiplication division modulo Addition subtraction James Tam Program Documentation Program documentation Used to provide information about a computer program to another programmer e Often written inside the same file as the computer program when you see the computer program you can see the documentation The purpose is to help other programmers understand how the program code was written how it works what are some of it s limitations etc User manual Used to provide information about how to use a program to users of that program e User manuals are traditionally printed on paper but may also be electronic but in the latter case the user manual typically takes the form of electronic help that can be accessed as the program is run The purpose is to help users of the program use the different features of the program without mention of technical details
3. James Tam Program Documentation 2 It doesn t get translated into binary It doesn t contain instructions for the computer to execute It is for the reader of the program What does the program do e g tax program What are it s capabilities e g it calculates personal or small business tax What are it s limitations e g it only follows Canadian tax laws and cannot be used in the US In Canada it doesn t calculate taxes for organizations with a yearly gross earnings over 1 billion What is the version of the program If you don t use numbers for the different versions of your program then consider using dates tie this with program features How does the program work e This is often a description in English or another high level language that describes the way in which the program fulfills its functions The purpose of this description is to help the reader quickly understand how the program works e Typically used to describe things that are not immediately self evident from the program code James Tam Program Documentation 3 Format lt Documentation gt The number sign flags the translator that what s on this line is documentation Examples Tax It v1 0 This program will electronically calculate your tax return This program will only allow you to complete a Canadian tax return James Tam Input The computer program getting information from the user Forma
4. 1 resets back to zero and column 2 For the next value increases by one column 1 resets back to zero and column 2 increases by one OADNABRWNeE SS Column 1 counts through all 10 possible values column 2 remains unchanged James Tam Decimal Summary Base ten Employs ten unique symbols 0 1 2 3 4 5 6 7 8 9 Each digit can only take on the value from 0 9 Once a column has traversed all ten values then that column resets back to zero as does it s right hand neighbours and the column to it s immediate left increases by one James Tam Binary Summary Base two Employs two unique symbols 0 and 1 Each digit can only take on the value 0 or the value 1 Once a column has traversed both values then that column resets back to zero as does it s right hand neighbours and the column to it s immediate left increases by one James Tam Counting In Binary Decimal value Decimal value James Tam How Is Binary Used Representing instructions in a computer program E g print End program onscreen translates to 0001 1000 1010 1111 0100 0101 0110 1110 Ete Representing the data in a computer program Alphanume
5. Getting Started With Python Programming eHow are computer programs created Representing information with binary Variables and constants Input and output Operators Common programming errors eAdvanced techniques for formatting text output Reminder About The Course Textbooks They re a recommended but not required However the course notes are required for this course Reminder How To Use The Course Resources They are provided to support and supplement this class Neither the course notes nor the text book are meant as a substitute for regular attendance to lecture and the tutorials James Tam Reminder How To Use The Course Resources 2 procedure add var head NodePointer var newNode NodePointer var temp NodePointer begin if head NIL then head newNode else begin temp head while temp next lt gt NIL do temp temp next temp next newNode end newNode next NIL end James Tam Reminder How To Use The Course Resources 2 procedure add vaxpead NodePointer i gode NodePointer cO PW 12 E 16 A ANKE newNode O O o Begin temp head while temp next lt gt NIL do temp temp next temp next newNode end newNode next NIL end James Tam How To Succeed Successful people Leonardo da Vinci J R R Tolkien Bruce Lee Amadeus Mozart Wayne Gretzky How To Succeed In This Course 1 Practice thi
6. ctangle length input Enter the length width input Enter the width area length width print Area area Advanced Text Formatting Triple quoted output Using escape sequences Triple Quoted Output Used to format text output eThe way in which the text is typed into the program is exactly the way in which the text will appear onscreen eYou can find an online example of triple quoted output in UNIX under home 231 examples intro formatting1 py From Python Programming 2 Edition by Michael Dawson James Tam Escape Codes eThe back slash character enclosed within quotes won t be displayed but instead indicates that a formatting escape code will follow the slash Escape sequence Description Alarm Causes the program to beep Backspace Moves the cursor back one space Newline Moves the cursor to beginning of the next line Tab Moves the cursor forward one tab stop Single quote Prints a single quote Double quote Prints a double quote Backslash Prints one backslash James Tam Escape Codes 2 eYou can find an online version of this program in UNIX under home 231 examples intro formatting2 py print a Beep print h bello print hi nthere print it s print he y you James Tam After This Section You Should Now Know The binary number system How to count in binary Conversions to from binar
7. cts Value in decimal 1x22 0x21 1x20 1x2 1 1x4 0x2 1x1 1 1 2 4 0 1 0 5 5 5 1 The value of this exponent will be determined by the position of the digit value of the superscript James Tam Binary To Decimal Other Examples 0101 11 222719 100000 2224 011111 222719 James Tam Decimal To Binary Split up the integer and the fractional portions For the integer portion Divide the integer portion of the decimal number by two The remainder becomes the first integer digit of the number immediately left of the decimal in binary The quotient becomes the new integer value Divide the new integer value by two The new remainder becomes the second integer digit of the binary number second digit to the left of the decimal Continue dividing until the quotient is less than two and this quotient becomes the last integer digit of the binary number James Tam Decimal To Any Base 2 For the fractional portion Multiply by two The integer portion if any of the product becomes the first rational digit of the converted number first digit to the right of the decimal The non rational portion of the product is then multiplied by two The integer portion if any of the new product becomes the second rational digit of the converted number second digit to the right of the decimal Keep multiplying by two until either the resulting fractional part of the product equals zer
8. ening quotes or brackets Using variables before they ve been named allocated in memory You can find an online version of this program in UNIX under home 231 examples intro syntax py print num James Tam 2 Runtime Errors Occur as a program is executing running The syntax of the language has not been violated each statement follows the rules syntax During execution a serious error is encountered that causes the execution running of the program to cease With a language like Python where translation occurs just before execution the timing of when runtime errors appear won t seem different from a syntax error But for languages where translation occurs well before execution the difference will be quite noticeable eA common example of a runtime error is a division by zero error 2 Runtime Error An Example eYou can find an online version of this program in UNIX under home 231 examples intro runtime py num2 input Type in a number num3 input Type in a number num1 num2 num3 print num1 3 Logic Errors The program has no syntax errors The program runs from beginning to end with no runtime errors But the logic of the program is incorrect it doesn t do what it s supposed to and may produce an incorrect result eYou can find an online version of this program in UNIX under home 231 examples intro logic py print This program will calculate the area of a re
9. hange print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange James Tam Named Constants And Python Using named constants is regarded as good style when writing a computer program Some programming languages have a mechanism for ensuring that named constants do not change Example A_ CONSTANT 100 With programming languages that enforce the A CONSTANT 12 immutability of constants this would result in an error Python does not enforce the immutability of constants so it is up to the person writing modifying the program to avoid changing the value stored in a constant James Tam Displaying The Contents Of Variables And Constants Format print lt variable name gt print lt constant name gt Example aNum 10 A_CONSTANT 10 print aNum print A CONSTANT James Tam Mixed Output eMixed output getting string output and the contents of variables or constants to appear together Format print string lt variable or constant gt string lt variable or constant gt etc Examples mylInteger 10 myReal 10 5 myString hello print MyInteger myInteger print MyReal myReal print MyString myString James Tam Arithmetic Operators Description Example Assignment num 7 Addition Subtraction Multiplication num 5 4 Division num 25 5 Modulo num 8 3 Exponent num
10. hat you wish to appear Example print foo print bar Variables Set aside a location in memory Used to store information temporary This location can store one piece of information At most the information will be accessible as long as the program runs Some of the types of information which can be stored in variables Integer Real numbers Strings Picture from Computers in your future by Pfaffenberger B Variable Naming Conventions Should be meaningful Names must start with a letter Python requirement and should not begin with an underscore style requirement Can t be a reserved keyword see next slide Names are case sensitive but avoid distinguishing variable names only by case bad style Variable names should generally be all lower case For variable names composed of multiple words separate each word by capitalizing the first letter of each word save for the first word or by using an underscore Be consistent Key Words In Python and del from not as elif global or assert else if pass break except import print class exec i raise continue finally i return def for try 1 From Starting out with Python by Tony Gaddis Constants Memory locations that shouldn t change The naming conventions for choosing variable names generally apply to constants but the name of constants should be all UPPER CASE You can separate multiple words with an undersco
11. ngs yourself You get better by doing things for yourself this is a hands on field of study and work Write lots programs e At the very least attempt every assignment e Try to do some additional practice work some examples will be given in class some practice assignments will be available on the course web page e Write lots of little test programs to help you understand and apply the concepts being taught Trace lots of code e Reading through programs that other people have written and understanding how and why it works the way that it does James Tam How To Succeed In This Course 2 2 Make sure that you keep up with the material Many of the concepts taught later depend upon your knowledge of earlier concepts Don t let yourself fall behind At least attempt all assignments Problem decomposition Loops repetition Decisions branching Introduction to programming Introduction to computers James Tam 3 4 How To Succeed In This Course 3 Look at the material before coming to lecture so you have a rough idea of what I will be talking about that day a Read the slides b Look through the textbooks if you got it James Tam How To Succeed In This Course 4 Start working on things as early as possible Don t cram the material just before the exam instead you should be studying the concepts as you learn them throughout the term Don t start assignments the night o
12. o or you have the desired number of places of precision James Tam Decimal To Any Base 2 ee g 9o to Stop dividing quotient less than target base James Tam Decimal To Binary Other Examples 5 75 2227 329 2272 3149 2272 Python e This is the name of the programming language that will be used to illustrate different programming concepts this semester My examples will be written in Python Your assignments will be written in Python e Some advantages Free Powerful Widely used Google NASA Yahoo Activision Electronic Arts etc e Named after a British comedy 4 Monty Python BBC e Online documentation http www python org doc 2 5 2 An Example Python Program eYou can find an online version of this program in UNIX under home 231 examples intro small py Filename small py print hello James Tam Creating Translating And Executing Python Programs _ To begin creating a Python program in Text editor e UNIX type XEmacs filename py oN Paton program filename py Text file Python translator ython To translate and execute the i Effect of execution program in UNIX type python e Message appears filename py onscreen File is opened Etc James Tam Displaying String Output String output A message appears onscreen that consists of a series of text characters Format print the message t
13. r day that they are due they may take more time than you might first think so start as soon as possible James Tam How To Succeed In This Course A Summary Practice things yourself Make sure that you keep up with the material Look at the material before coming to lecture Start working on things early James Tam Computer Programs Binary is the language of the computer Translator do e g python 3 An executable 1 A programmer program is writes a computer 2 A translator created program N converts the program into a form that the fhe 4 ikk A computer can a l P understand 4 Anybody who has this executable installed on their computer can run use it James Tam What Is Binary What you know Binary is a method of representing information that uses two states What you may not be aware of The number system that you are familiar decimal uses 10 states to represent information How Is Decimal Used To Store Numeric Information Base 10 The number of digits is 10 unique symbols are used to based on the number of represent values digits 3 2 74 b j j The largest decimal value that can be represented by a single decimal digit is 9 base 10 1 How Does Counting In Decimal Work Column 1 counts 18 through all 10 19 possible values 26 column 2 remains Column 1 unchanged counts through all 10 possible For the next value values column
14. re They are capitalized so the reader of the program can distinguish them from variables For some programming languages the translator will enforce the immutability of the constant For languages such as Python it is up to the programmer to recognize a constant for what it is and not to change it James Tam Why Use Constants They make your program easier to read and understand populationChange 0 1758 0 1257 currentPopulation Magic Numbers avoid whenever BIRTH_RATE 17 58 possible MORTALITY_RATE 0 1257 currentPopulation 1000000 populationChange BIRTH_RATE MORTALITY_RATE currentPopulation James Tam Purpose Of Named Constants 2 e2 Makes the program easier to maintain e If the constant is referred to several times throughout the program changing the value of the constant once will change it throughout the program James Tam Purpose Of Named Constants 3 BIRTH_RATE 0 1758 MORTALITY_RATE 0 1257 populationChange 0 currentPopulation 1000000 populationChange BIRTH_RATE MORTALITY_RATE currentPopulation if populationChange gt 0 print Increase print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange elif populationChange lt 0 print Decrease print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange else print No change print Birth rate
15. ric text is represented with a numeric code decimal ASCII value which is translated to a binary ASCII value e g A 65 0100 000 In UNIX type man ascii for all the ASCII codes Signed integers can be represented by using one bit representing the sign of the number and the remainder of the bits representing the size of the number Sign bit Remaining bits n 1 0 positive Used to represent the 1 negative size of the number James Tam How Is Binary Used 2 Signed real numbers are more complex and require three parts Sign bit Mantissa bits Exponent bits Le The mantissa is raised to the exponent in order to determine the size of the number Example F Two Positive Three Number Positive 2 cubed the number positive 8 is being represented in signed binary James Tam Why Is It Important To Know How Data Is Being Stored Different representations store different types of information but some have drawbacks Real number representations may result in a loss of accuracy Only an approximation of some fractional values may be stored e g 1 3 Even storing some non repeating fractional values may result in the loss of some information Example suppose 1 digit is used for the sign 5 for the mantissa and 3 for the exponent e 123 45 is represented as 12345 10 0 12 is represented as 12000 10 5 e 123456 is represented as 12345 10 Morale of the story Don t store info
16. rmation as a real number if it can be stored as an integer because of the potential loss of accuracy e g store monetary values as cents rather than dollars James Tam Storing Other Information eText ASCII represents simple alphanumeric information 8 bits 1 used for error checking 7 for the alphanumeric information 128 combinations eText beyond simple English representations Arabic Dutch Chinese French German etc Representing this expanded text information uses additional bits e 16 bits 65 536 combinations 24 bits 16 777 216 combinations James Tam Storing Other Information 2 Colors using 16 million colors can present a true life representation how are the color combinations encoded James Tam Converting From Binary To Decimal eStart with some binary number to convert E g 101 1 Label each of the binary digits Starting with the digit immediately left of the decimal point and moving left away from the decimal point label the binary digits 0 1 2 3 etc in succession Starting with the digit immediately right of the decimal point and moving right away from the decimal label the binary digits 1 2 3 2 1 0 1 4 Position of each binary digit E g 101 1 lt Binary number to be converted Evaluate the expression the binary digit raised to some exponent multiply the resulting expression by the corresponding digit and sum the resulting produ
17. t lt variable name gt input OR lt variable name gt input lt Prompting message gt Example print Type in a number num input OR num input Type in a number James Tam Types Of Programming Errors 1 Syntax translation errors 2 Runtime errors 3 Logic errors James Tam 1 Syntax Translation Errors Each language has rules about how statements are to be structured eAn English sentence is structured by the grammar of the English language The cat sleeps the sofa Grammatically incorrect missing the preposition to introduce the prepositional phrase the sofa Python statements are structured by the syntax of Python 5 num Syntactically incorrect the left hand side of an assignment statement cannot be a literal unnamed constant James Tam 1 Syntax Translation Errors 2 The translator checks for these errors when a computer program is translated to binary For compiled programs e g C C Pascal translation occurs once before the program is executed because compilation occurs all at once before execution For interpreted programs e g Python translation occurs as each statement in the program is executing because interpreting occurs just before each statement executes James Tam 1 Some Common Syntax Errors Miss spelling names of keywords e g primt instead of print Forgetting to match closing quotes or brackets to op
18. y The different ways in which information is represented using the binary system eHow to create translate and run Python programs on the Computer Science network Variables What they are used for How to access and change the value of a variable Conventions for naming variables Named constants What are named constants and how do they differ from variables What are the benefits of using a named constant James Tam After This Section You Should Now Know 2 What is program documentation and what are some common things that are included in program documentation How are common mathematical operations performed Output How to display messages that are a constant string or the value of a memory location variable or constant onscreen with print Input How to get a program to acquire and store information from the user of the program eWhat are the three programming errors when do they occur and what is the difference between each one eHow triple quotes can be used in the formatting of output eWhat is an escape code and how they can affect the output or execution of a program James Tam
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