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# while loop - countdown

## Introductory Problem

Ask the user what food they would like to eat everyday. Using a while loop, print their favorite food 5 times.
intro.py
x = 0
food = input("What type of food do you like to eat? ")
while x < 5:
print(food)
x = x + 1

## while loop

A while loop executes an indented block of code, or instructions, repeatedly while a condition is true. Previously, you learned about if statements that executed an indented block of code while a condition was true. You can think of a while loop like an if condition but the indented block of code executes more than once. Hence, a loop. ## Variable Roles

Recall that a stepper variable iterates, or loops, a specific number of times. Programmers use`x`or`i`as a stepper variable.

## while loop Examples

### Example 1

Rewrite the Do Now to print the user’s favorite food 5 times by decrementing the variable rather than incrementing.
Steps:
• Initialize the stepper variable x to 5.
• Ask the user what they like to eat everyday.
• Using a while loop, create a condition that will execute 5 times.
• Print variable.
• Decrement the stepper variable.
example1.py
x = 3
food = input("Favorite Food: ")
while x > 0:
print(food)
x = x - 1

### Example 2

Using a while loop, print even numbers from 10 to 1.
What value can we initialize the stepper variable to?
example2.py
x = 10
while x > 0:
print(x)
x = x - 2

### Example 3

Using a while loop, ask the user for a number 3 times. Where in the program should we ask the user for the number? Inside the loop, or outside the loop?
Create a temporary variable named squared that squares the number. Create another temporary variable named cubed that cubes the number.
Print the values of squared and cubed.
example3.py
x = 3
while x > 0:
num = int(input("Number: "))
squared = num * num
print("Squared:",squared)
cubed = num ** 3
print("Cubed:",cubed)
x = x - 1

### Example 4

You eat a Pepperoni Pizza slice which is 400 calories and now want to burn off these calories for 10 minutes. You burn 11 calories per minute running. Create a chart to represent how many minutes you have left to exercise and how many calories you have left to burn off.
Steps:
• Create a variable named calories and initialize it to 400.
• Before the while loop, add the following lines to create your chart.
• print("Mins\tCalories")
• "\t" means tab.
example4.py
print("Mins\tCalories")
calories = 400
x = 10
while x >= 0:
print(x,"\t",calories)
calories = calories - 11
x = x - 1

## Conclusion

• In your own words, what is a while loop? What is a real life example when you count down?
• Explain the role of the stepper variable when the while loop counts down.