While loop

Unsure how many times to repeat code?

Python has the while keyword. Unlike the for loop which tests the condition first, the while loop execute the code first. Sometimes we don’t know how long sometimes will take.

A theoretical program could be (pseudocode):

which keeps executing the code block until the condition is true.

Related Course:

while loop example

Lets build an extended ‘guess the number game’:

This will keep asking a number until the number is guessed.   This is defined in the line: while x != 5, or in English,  “while x is not equal to five, execute”.

Illustrated:
while loop

The program keeps repeating the code block while the condition (x!=5) is True. Once x equals 5, the program continues.

Infinite loops

If a condition in a while loop is never met, it could cause the program to run forever or to freeze/crash.
 

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2 Replies to “While loop”

  1. Ok…..I give…..what terminates the WHILE LOOP? I’m not asking when the loop condition changes, what terminates the code contained in the WHILE loop? Is it simply formatting? (TAB positions)

    • Without the condition being true, it will continue forever (or until memory overflow). The break keyword can make it stop as well. In most of the cases, you want to be sure the while loop condition is met. Some while loops should last forever except if the machine is turned of, like a web server or computer game.

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