Python - Introduction to While Loops

Python - While Loops

While Loops

A while loop is a block of code that will keep repeating until a condition has been met.

Looping (Iteration)

• Looping code in programming is called "Iteration"

• You can re-use the same code over and over again.

• This saves on the amount of code you have to write.

Example

• This example asks you what the capital city of France is.

• It keeps asking the same question if your answer is not Paris.

Multiple Choice

In programming, what is iteration?

• The repetition of steps within a program
• The order in which instructions are carried out
• A decision point in a program
• Testing a program to make sure it works

Multiple Choice

Why is iteration (looping) important?

• It determines the order in which instructions are carried out

• It allows code to be simplified by removing duplicated steps

• It allows multiple paths through a program

• It ensures the code works correctly

Conditions that cause and stop a loop.

Loops can sometime be stuck in an infinite loop

This can be fixed by asking for a user input for the variable "play" during each loop.

The loop will carry on if you type "yes" (meeting the condition)

Typing anything else will stop the loop.

Using a Counter

This loop will print out "Let's play" each time is runs.

After every loop, the counter increases by one.

It continue to loop while the counter is less than 5

What happens when the counter reaches 5?

Multiple Choice

How many times will this program print out "Let's play before the loop stops?"

• 4

• 5

• 0

• 9

Whay was the answer 5 times?

• The counter for the loop begins at 0.

• the looping happened when the counter was 0,1,2,3 and 4

Multiple Choice

How many times will this loop run before it exits?

• 3

• 5

• 4

• 10

Conditions

• Equal to ==

• Less than <

• Greater Than >

• Less than or equal to <=

• Greater than or equal to >=

• Not equal to !=

Multiple Choice

The condition for a while loop to continue could include which of the following?

• While something equals something
• While something is greater than something
• While something is True
• All of these

Multiple Choice

Which of the following symbols is used in Python to mean "Greater than or equal to"?

• <=
• >>
• >=
• =>

Multiple Choice

Which of the following symbols is used in Python to mean "Not equal to"?

• ==
• !=
• <>
• ><

Multiple Choice

Which of the following symbols is used in Python to mean "Equal to"?

• =
• !=
• ==
• >=

Multiple Choice

Which type of loop iterates (loops) until instructed otherwise?

• FOR loop

• A count-controlled loop

• Repeat-once loop

• WHILE loop

Using "break" to end a loop

In this example, the loop is still set to run 5 times.

On each loop you are asked the question "what is 2+2".

If you answer correctly, you are told "correct" and the loop breaks.