while loop - countdown

Introduction
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 usexorias 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
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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.
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Problems

Examples

Last modified 3yr ago