While Loops

A while loop repeats a block of code as long as a condition is true.

Basic Structure

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

Output:

Note: The indented code runs repeatedly until the condition becomes False.

Infinite Loops with `while True`

Use while True: to create a loop that runs forever (until you break out of it):

while True:
    answer = input("Type 'quit' to exit: ")
    if answer == "quit":
        break
    print("You typed: " + answer)

The break statement immediately exits the loop.

The `break` Statement

Use break to exit a loop early:

count = 1
while count <= 10:
    print(count)
    if count == 5:
        print("Stopping early!")
        break
    count = count + 1

Output:

1
2
3
4
5
Stopping early!

The `continue` Statement

Use continue to skip to the next iteration:

count = 0
while count < 5:
    count = count + 1
    if count == 3:
        continue  # skip printing 3
    print(count)

Output:

Input Validation Example

A common use of while loops is to keep asking until the user gives valid input:

color = ""
while color != "red" and color != "blue":
    color = input("Pick red or blue: ")
print("You picked " + color)

Game Loop Example

Many games use while True: as their main loop:

health = 100

while True:
    print("Health: " + str(health))
    action = input("Attack or run? ")

    if action == "run":
        print("You escaped!")
        break
    elif action == "attack":
        health = health - 10
        if health <= 0:
            print("Game over!")
            break

Common Mistakes

Forgetting to update the loop variable

# Wrong - infinite loop!
count = 1
while count <= 5:
    print(count)
    # Oops, forgot to increase count

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

Forgetting the colon

# Wrong
while count <= 5
    print(count)

# Right
while count <= 5:
    print(count)

Incorrect indentation

# Wrong - print is not inside the loop
while count <= 5:
print(count)

# Right
while count <= 5:
    print(count)