UNIT 6. Functions and Structured Programming

Transcription

1 UNIT 6 Functions and Structured Programming

2 DAY 1 What is a Function? What is Structured Programming?

3 I can.. Divide a large program into small problems. Write a Python program as a function

4 Planning a Wedding What are some of the steps we will take when planning a wedding?

5 Planning a Wedding Make Guest List Take Engagement Photos and Send out Save the Dates Decide on Wedding Party Find Wedding Gown, Bridesmaid Dresses, and Tuxes Pre-Marital Meeting with Officiant (Paster, Priest, etc) Food Tasting Purchase Decorations Plan Rehearsal Dinner Do Final Preps Decorate the Hall Prepare Food Dance and Enjoy!

6 What is Structured Programming? Organizing programs by breaking them up into smaller, easier to manage programs (called functions) Allows you to reuse code that is repeated! Divide and Conquer Method Top Down Design Break a large programming task (Top) into smaller and smaller subtasks (Bottom) **ALSO CALLED MODULAR PROGRAMMING**

7 Why is Structured Programming Needed? Past programming: Programming in older languages vs. modern style of programming Older: Spaghetti Code Hopelessly intertwined statements caused by numerous jumps between sections of code Nearly impossible to follow NO FLOW Modern: Use functions 1 main function where main code runs logically in order Will run other functions but always return to main.

8 Steps to Writing a Structured Program 1. Start with an Outline of the main program Write out pseudocode to describe major tasks to be performed Avoid thinking about the details of each major task right now 2. Write the main - mostly calls to functions Translate each English phrase into one or two function calls Use documentations to describe the actions and make programs readable

9 Steps to Writing a Structured Program 3. Write each function Define the function (name and parameters) Type the code for that function (indented) 4. Test and Debug Use a complete set of test data to be sure it works Make changes or refinements that are necessary or desireable

10 Example of the planning process

11 We ve Already Used Functions Brain storm as many functions as you can that we ve already used throughout this semester!

12 Functions Already Used Turtle graphics. forward() color() left() goto(x, y) Math functions sqrt(n) pi pow(b, n) floor(n) General Functions print() input() eval() String Functions len(x) upper(x) chr(x) ord(x) split(x) Random Functions random() randrange(x,y,z) randrange(x, y) **We ve actually used MORE than this**

13 What is a function? A sub-program or block of code that accomplishes a specific task Often returns a value, text, or object A Mini Program Also called a method or subroutine

14 New Approach to the Main Function We can (and will starting today) write our main function like a function! Functions Syntax: def <name of function> (): <statements>

15 Let s Write an Example Together Let s write a program that prints out the lyrics to the song Happy Birthday Main program must now be written as a function so we can add functions in later!

16 Program #1 # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) # print happy birthday to user print( Happy Birthday to you ) print( Happy Birthday to you ) print( Happy Birthday dear, name) print( Happy Birthday to you )

17 How do we make our program run? The main function is an executable function but we need to tell it to execute the main! def main () : <statements>.. main() This line of code at the end of a python program will run the main function

18 Let s Write our First Function In the happy birthday program do you notice any code repeating??? This is a perfect time to use a function!

19 Let s Look Back! # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) main() # print happy birthday to user print( Happy Birthday to you ) print( Happy Birthday to you ) print( Happy Birthday dear, name) print( Happy Birthday to you ) repeated 3 times repeated 3 times repeated 3 times

20 Let s Write a Function **Add this code beneath the main() statements** # function prints 1 line of Happy Birthday def happy (): print( Happy Birthday to you )

21 Let s Update our Main! # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) main() # print happy birthday to user happy() happy() calling and running the happy() function calling and running the happy() function print( Happy Birthday dear, name) happy() calling and running the happy() function

22 Program Write a program to print the lyrics to the song Old MacDonald. Your program should use functions for any repeated line of code. Write your program so it will sing Old Mac Donald for three different animals: Basic Verse: Old Mac Donald had a farm! Ee-igh-ee-igh-oh! And on that farm he had a cow! Ee-igh-ee-igh-oh! With a moo, moo here and a moo, moo there! Here a moo, there a moo, everywhere a moo, moo! Old Mac Donald had a farm! Ee-igh-ee-igh-oh!

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24 DAY 2 Passing parameters to a function

25 I can.. Write a function in Python. Write a program that uses functions

26 Review of Terminology: What is a function? What is structured programming? What is structured programming also called? What are the benefits of structured programming?

27 Benefits of Structured Programs 1. Easier to read Each function will have documentations explaining its purpose 2. Easier to write Complicated programs broken down into smaller, easier to manage functions 3. Easier to use, change, adapt, modify, debug Only need to change in one location (not every time appears in program) Easily determine where an error is occuring 4. Easier to reuse Can be copied into another program Can be called in the same program multiple times 5. Other, More powerful programming languages require this kind of structure.

28 Writing Python Programs with Functions! def main(): <statements> function1() function2() def function1(): <statements> def function2(): <statements> main()

29 Question to Ponder 1. If each function is its own mini program, how is information shared between different functions? 2. How do I get data that is held within one subroutine into another one for processing??

30 Parameter Variable Values passed into the function The function needs these values in order to do its job May include as many parameters as the function needs If no parameters are needed the parentheses are empty **Yesterday s happy() function**

31 Parameter Passing A function definition with parameters: def <name> (<formal parameters>) : <statements> Example: def hello (person) : print( hello, person)

32 Parameter Passing A function call with parameters: <name>(<actual parameters>)

33 Parameters The parameter provides a method of transferring data from the main function to be the function being called Ex: ord( A ) chr(45) lower(message) takes in a CHARACTER takes in an INTEGER takes in a STRING

34 Let s update our Happy Birthday Program Version 1: Create a function called sing that will take in a parameter name and sing happy birthday to the person The Sing function should use the happy() function we create yesterday Program should sing Happy Birthday to Joe, Callie, and Alex

35 Let s update our Happy Birthday Program # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) main() # print happy birthday to user happy() happy() print( Happy Birthday dear, name) happy()

36 Sing Function # Sings happy birthday to a person with a given name def sing (personname): happy() happy() print( Happy Birthday dear, personname) happy()

37 How do we call a function with parameters? The same way we call any other function but we need to ensure we send it that parameter requirements Example: sing(personname)

38 Let s update our Happy Birthday Program # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) #sings happy birthday to user sing(name) # sends in name of user main()

39 Let s Sing to More People! # Happy Birthday Program # create main function def main (): # get name from user name = input( What is your name?: ) main() #sings happy birthday to user and others! sing(name) # sends in name of user sing( Joe ) sing( Callie ) sing( Alex )

40 Write a Program in Python that contains the following. Your program will: 1. Call a function which prints a welcome message. 2. Call a function which sends the user s name and comments to the user telling him/her how many characters are in the name 3. Calls a function which sends the user s age and comments on whether the user is able to drive or not. 4. Calls a function that sends in the user s favorite color and comments on the color. 5. Calls a function that generates a random number for the user and prints the number to the screen. 6. The user should be able to continuously play this game until they choose to quit.

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42 DAY 3 Returning a Value

43 I can.. Write a function in Python that returns a value. Write a program that uses functions

44 Review of Terminology: What is a function? What is structured programming? What is structured programming also called? What are the benefits of structured programming?

45 How do we get a value from a function? Most functions we have used so far in this class have provided us with a value. Examples: len() lower() returns the number of characters in a string returns a copy of a string in all lower case letters randrange(4,9) returns a random integer between 4 and 8 ord() chr() returns a character at the ASCII number returns an integer for the ASCII character

46 Returning a Value Called Function returns a value to the program calling the function. If a value is returned, it must either be saved inside a variable in the program calling the function or used immediately when called If the returned value isn t saved or used, it is LOST Function are NOT required to return a value

47 Returning a Value Returning a Value def <name> (<formal parameters>) : <statements> return <variable name>

48 Returning a Value Example in Code def addition(num1, num2): sum = num1 + num2 return sum

49 Program: Convert Pounds to Kilograms # main program def main(): #welcome statement print( Converts pounds to kilograms \n \n ) # gets weight from user lbs = eval(input( Enter your weight in lbs: ) # converts pounds to kilograms, returns kgs, and # SAVES the value inside a new variable named kgs kgs = compute(lbs)

50 Program continued # prints kilograms to screen print(weight in kgs:,kgs) # function that converts pounds to kilograms def compute(lbs): kilograms = lbs/2.2 return kilograms #runs main program main()

51 2 nd Way to Use returned values # main program def main(): #welcome statement print( Converts pounds to kilograms \n \n ) # gets weight from user lbs = eval(input( Enter your weight in lbs: ) #prints kgs to screen print(weight in kgs:, compute(lbs) )

52 Write a Program that does the following 1. Write a program that converts between Fahrenheit and Celsius (C=(F-32)*5/9). Your program must use a function to calculate the temperature in Celsius and return the value to the main function to be output. 2. Write a program that asks the user for a number and then calculates the square of that number. Your program must use a function to calculate the square and return the value to the main function to be output.

53 Write a Program that does the following 3. Write a program that will find the area of a sphere (A=4*pi*r 2 ) with a radius provided by the user. Your program must use a function and return the area of the sphere to the main function to be output. 4. Write a function that calculates the sum of the first n natural numbers. N is a value that will be inputted by the user and should be used passed into a function that calculates the sun of the numbers from 1 to n. Your function must return a value to be outputted.

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55 DAY 4 Passing more than one Parameter

56 I can.. Write a function in Python that takes in multiple parameters.

57 Review of Terminology: What is a function? What is structured programming? What is a parameter? What is a returned value?

58 What happens when we send in a parameter? Main function (or the function calling another function to run) sends in the VALUE This means if a variable name is placed in the parameter list, the VALUE is the only thing sent in THE VARIABLE VALUE WILL NOT BE CHANGED IN THE MAIN PROGRAM AS THE FUNCTION FUNS The variable value sent in will only be USED by the function to complete its task

59 Example def main(): name = input( What is your name: ) double(name) print(name) def double(name) : name = name*2 print(name) main()

60 Functions Using Parameters name name Each function stores its local variable information in different places in memory In this program there are actually 2 variables called name one saved in the main program s block of memory another stored in the double function s memory

61 Local Variable All variables are LOCAL to the function they are defined in. **Bubbler Explanation Example** To access a variable outside a function, it must be passed to the function

62 Passing Parameters Function Definition Syntax: def <name>(<formal parameter1>,, <formal parametern>) <body> Function Call Syntax: <name>(<actual parameter1>, <actual parametern>)

63 Passing Parameters by VALUE A copy of the VALUE of a variable are passed to the function. The function than creates it s own variable with that value this variable is LOCAL to the function

64 When Python Comes to a Function Call 1. The calling function suspends execution at the point of the call 2. The formal parameters of the function get assigned the values supplied by the actual parameters in the call. 3. The body of the function is executed. 4. Called function returns a value (if necessary) and the program returns to the point just after where the function was called.

65 Example Program #1 def main() : print( The value of x in main before the function call, x) changex(x) print( The value of x in main after the function call, x) def changex(x) print( The value of x at beginning of changex call, x) x = x + 25 print( The value of x after changex call, x) main()

66 Example Program #2 def() main: length = eval(input( Enter length: )) width = eval(input( Enter width: )) area = computearea(length, width) print( area =, area) def computearea(l, w) : a = l*w return a main()

67 Write a Program that does the following 1. Write a program that takes in two numbers from the user. Then write two function one that finds the SUM of the two numbers and one that finds the DIFFERENCE of the two numbers. Both functions should take in two parameters and return a value to the main program. 2. Write a program that takes in five numbers from the user (representing the 5 sides of a pentagon). Then write a function to find the PERIMETER of the pentagon. This function should take in the side lengths as parameters and return the perimeter to the main program. 3. Write a program that takes in three numbers from the user and finds the average. This program should contain a function that takes in three values as parameters and returns the average to the calling program.

68 Write a Program that does the following 4. Write a program that takes in the lengths of the two bases and the height of a trapezoid and calculates its area. This program should contain a function that takes in the three values as parameters and returns the area (A = ½ *h*(b1+b2)) 5. Write a program that takes in three numbers from the user (3 side lengths of a triangle). Then write a function that finds the area of the triangle using Heron s formula below (s = half the perimeter and is used to find the area). s = (a + b + c) / 2 A = s(s - a)(s - b)(s - c)

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70 DAY 5 Combining Structure Programming with Control Structures (if and loops)

71 I can.. Use control structures (loops and conditionals) with function calls.

72 Example Program 1 Roll two dice until get a roll of 2 (snake eyes each die is a 1) Track how many rolls it takes to roll snake eyes Print the number of rolls to the screen

73 Example Program 1 - Code from random import randrange def main(): roll = 0 rolltotal = 0 while rolltotal!= 2 : rolltotal = rolldice() roll = roll + 1 print( It took, roll, rolls to get snake eyes )

74 Example Program 1 Code (pg 2) def rolldice(): roll1 = randrange(1, 7) roll2 = randrange(1, 7) rolltotal = roll1 + roll2 return rolltotal main()

75 Example Program 2 Takes in a number States whether the number is even or odd (using a function)

76 Example Program 2 - Code def main(): number = eval(input( Please enter in a number: )) evenodd = evenorodd(number) print( Your number is, evenodd) def evenorodd(number): if number%2 == 0: return even else : return odd main()

77 Write a Program that does the following 1. Write a program that takes in 2 numbers from a user. Your program should then send these two values into a function as parameters. The function should find the sum of ALL of the numbers between these two values. **Extension have a second function to calculate the sum of all the odd numbers and a third function to calculate the sum of all the even numbers between these as well** 2. Write a program that find the average of 5 test scores. Your program should have one function that finds the sum of all 5 test scores and returns the sum to the main program. Your program should then have a second function that finds the average of all the test scores and returns the average to the main program.

78 Write a Program that does the following 3. Write a program that finds the slope between two points entered in by the user (x1, y1) and (x2, y2). Your program should have a function that checks whether x1 and x2 are the same. If the are, the slope should not be calculated (0 in denominator will throw an error). If they are NOT the same, the slope of the line should be calculated. Use the equation below. Slope = y2 y1 x2 x1 4. Write a program that simulates a coin flip. The user of the program should enter in how many times a coin should flip. Your program should have a function that simulates a coin flip and returns the result of a flip. **Extension design your program so that it will ask the user if they want to play again after the simulation has occurred. If they choose to play again the program will run again with all values reset, if they choose to quit the game will simply end.

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80 Program 5 How many items did you buy Cycles through item prices and finds sum Asks for tax Calculates total cost Asks user if they want to play again Widgets and Dodads project

81 EXTRA Write a program that draws a circle to the screen. The program should take in an (x, y) coordinate for the center of the circle, the radius, and the color of the circle from the user. This program should then contain a function that takes in these parameters and draws the appropriate circle to the screen.