As mentioned in the video, a while loop is a mechanism to allow you to repeat set of steps many times as long as a certain condition is true. For example, you may want to heat up leftover pizza in the microwave as long as it$$s too cold. The pizza starts out too cold. So you put it in the microwave for $30$ seconds. Then you check if it$$s still too cold. Then put it in for another $30$ seconds. Check if it$$s still too cold. Repeat this process until it is warm enough $($the cheese is melted$).$

The procedure, written in a Python like pseudocode would look like this:

temp $=$ get temperature of pizza

while temp is too cold:

heat in microwave for $30$ seconds

temp $=$ get new temperature of pizza

All while loops have these three elements:

an initial condition, usually involving initialization of a loop control variable. $($temp in this case$)$

a Boolean condition that is tested each time through the loop to determine whether the loop body $($the statements indented under the while statement$)$ will be run or not. temp is too cold is a True or False statement that is our Boolean condition.

a statement at the bottom of the loop that will potentially change the loop control variable temp $=$ get new temperature of pizza.

Like branching statements, while loops are code blocks using indentation. An if statement has

if boolean$\_$condition:

# indented statements

# to execute when the condition is True

A while loop has

while boolean$\_$condition:

# indented statements

# that will be executed

# as long as the condition is True

# a statement to potentially change the boolean$\_$condition

While Loop Syntax

While loops use a : after the condition and indent for all commands that should be repeated when the condition is true. Here is a while loops that prints $$Hello$$ five times.

count $=0$ # count is the loop control variable

while count $<5$: # count $<5$ is the Boolean condition

print$("$Hello$")$

count $=$ count $+1$ # the loop control variable is changed

Code Visualizer

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What happens if you:

Change the while statement to while count $<10$:$?$

Change the last line of code to count $=$ count $+2?$

Change the while statement to while count $<0$:$?$

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