While Loop

Understanding the while Loop

A while loop repeatedly executes a block of code as long as a given condition remains True.

It is ideal when:

• The number of iterations is not fixed.
• Repetition depends on a condition that changes over time.
• You want to loop until a certain state is reached.

Structure of a While Loop

A proper while loop requires three parts:

Syntax

i = starting_value   # Initialization

while condition:      # Condition
    statements
    i += 1            # Update

Examples of While Loops

Example 1 — Basic Loop

i = 1
while i <= 5:
    print("Hello World")
    i += 1
print(i)

Output:

Hello World
Hello World
Hello World
Hello World
Hello World
5

Example 2 — Decrementing Loop

i = 5
while i >= 1:
    print("Telusko")
    i = i - 1

Output:

Telusko
Telusko
Telusko
Telusko
Telusko

Example 3 — Printing Counter Values

i = 5
while i >= 1:
    print("Telusko", i)
    i = i - 1

Output:

Telusko 5
Telusko 4
Telusko 3
Telusko 2
Telusko 1

Infinite Loops

A while loop without an update or with a condition that is always True can cause your CPU usage to spike.

Example of an infinite loop:

while True:
    print("Hello")

This loop never ends because the condition is always True.

Using the end Parameter in print()

By default, print() ends with a newline (\n). You can change this behaviour using end.

Syntax:

print(value, end=' ')

Example

i = 1
while i <= 5:
    print("Telusko ", end="")
    print("Rocks!! Rocks!! ")
    i += 1
print(i)

Output (single line per loop):

Telusko Rocks!! Rocks!!
Telusko Rocks!! Rocks!!
Telusko Rocks!! Rocks!!
Telusko Rocks!! Rocks!!
Telusko Rocks!! Rocks!!

Nested While Loops

A nested while loop means having one loop inside another. The inner loop completely executes for every iteration of the outer loop.

• To make the nested loop work correctly for each iteration of the outer loop, we reset j inside the outer loop:

Example

i = 1
while i <= 5:
    print("Telusko ", end="")
    j = 1
    while j <= 4:
        print("Rocks!! Rocks!! ", end="")
        j += 1
    i += 1
    print()

Output:

Telusko Rocks!! Rocks!! Rocks!! Rocks!!
Telusko Rocks!! Rocks!! Rocks!! Rocks!!
Telusko Rocks!! Rocks!! Rocks!! Rocks!!
Telusko Rocks!! Rocks!! Rocks!! Rocks!!
Telusko Rocks!! Rocks!! Rocks!! Rocks!!

• Each Telusko is now followed by 4 Rocks lines.

If you do not reset the inner loop variable (j) inside the outer loop, the inner loop will run only once, not repeatedly.

When to Use a While Loop?

Examples:

• Continuously taking user input until they press ‘exit’
• Waiting for a file to be created
• Repeating tasks until a certain condition becomes False

Summary

• A while loop repeatedly executes a block of code as long as its condition evaluates to True.
• The loop variable must be initialized before the loop begins to ensure proper execution.
• The condition determines how long the loop continues and when it should stop.
• The loop variable must be updated (incremented or decremented) inside the loop to avoid infinite execution.
• Nested while loops involve an inner loop that runs completely for each iteration of the outer loop.
• The end parameter in print() controls output formatting by deciding whether to print on the same line, add spaces, or move to a new line.