Warm-up

• Get a name from the user.
• If the user didn't enter a name, print "you didn't enter a name!"
• Otherwise, print a greeting to the user.

Lesson 2.4

Introduction to While Loops

Why Loops?

• Let us repeat code without copying and pasting
• Useful when we don’t know how many times to repeat
• while checks a condition and keeps going as long as it’s True

Syntax of a while loop

while condition:
    # code that repeats while condition is True

Example

count = 1
while count <= 5:
    print(count)
    count = count + 1

• Prints 1 through 5

Important: Indentation

• All code inside the loop must be indented
• Each cycle is called an iteration

Infinite Loops

while True:
    print("This never stops!")

• Always check that your loop condition will eventually become False

Classroom Question

What will this print?

x = 3
while x > 0:
    print(x)
    x = x - 1
print("Done!")

Practice Challenge

Write a program that:

• Asks the user for a password
• Keeps asking until they type "python"
• Then prints "Access granted"