Iteration

 

Most programs need some process to be repeated many times. A process usually needs many lines of code. To avoid having to write that part of the code many times, the Repeat Structure is used. This comes in two basic forms:

 

• Test first loop - unknown number of loops
• Fixed number of loops

 

Common boolean operators

• > Greater than
• < Less than
• >= Greater than or equal to
• <= Less than or equal to
• == Equal to
• != and <> Not equal to

 

Test First Loop

 

Getting a part of a program to repeat using a Test First Loop structure.

 

The Test First Loop gives the option to enter into a code segment, and continue using this code until a condition is met. The code may never be activated if the appropriate condition is met.

 

The general form is:

 

While condition expression:

… statements

 

 

The loop condition controls the outcome and must be a Boolean expression. An example would be Age < 6 where Age is a variable, < is a boolean operator and 6 is a test value.

 

Example - simple guessing game

 

 # simple guessing game

secret = 12

guess = int(raw_input("Guess the secret number <0..100> -> "))

 

# Loop until the number is guessed

while (guess != secret):

    guess = int(raw_input("Guess the secret number <0..100> -> "))

 

#output

print 'You guessed it.'

 

Note:

• The secret number is set as an integer value
• The value for guess is read as a string and so needs to be converted to an integer for comparison

 

Fixed Loop Structure - For .. Next Structure

 

Sometimes it is necessary to repeat a section of code a set amount of times. The For..Next loop structure is used to handle these problems. It has a "built in" counter that is automatically increased as the code is repeated.

 

Example - add up scores of members of a cricket team (11 players)

 

#Adding up scores written in Python

#adds up 11 scores

 

print 'Cricket Scores.' #program heading

 

#initialise total

total = 0

 

#use the range function to set up team list of 11 players

team = range(1,12)

 

for player in team:

    score = int(raw_input('Enter a score for player ' + repr(player) + ' -> '))

    total = total + score

    print 'Total so far is %d' %(total)

 

print 'You have finished.'

 

Exercises

 

1. Don Ladly, coach for the Bilby footy team, needs a program that will add up the goals kicked by a given player  over the season. Write a program that will accept the player's name and the goals kicked each game (if any) and display a message such as "Bill Jones kicked 65 goals this season".
2. Bunnys hardware needs a program that will allow stock control of a paint sale where 80 cans of paint are available. Write a program that will allow the check-out operator to enter the number of cans purchased and advise when no more paint is left.
3. Write a program that will show a list of the temperatures from 0-20 degrees celcieus in farenheit

 

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