Introduction to Loops

Loops allow you to repeat a block of code multiple times, making your programs more efficient and concise.

In this lesson, you’ll learn about different types of loops in Python: for, while, and nested loops.

What is a Loop?

A loop is used to execute a block of code repeatedly until a certain condition is met. For example:

This prints the numbers 0 to 4.

# Example of a loop
for i in range(5):
    print(i)

The for Loop

The for loop iterates over a sequence (like a list or range) and executes a block of code for each item:

# Example of a for loop
names = ["Alice", "Bob", "Charlie"]
for name in names:
    print("Hello,", name)

The while Loop

The while loop continues to execute a block of code as long as its condition is True:

# Example of a while loop
counter = 0
while counter < 3:
    print(counter)
    counter += 1

Breaking Out of a Loop

You can use the break statement to exit a loop prematurely:

This stops the loop when i is equal to 5.

# Using break to exit a loop
for i in range(10):
    if i == 5:
        break
    print(i)

Skipping Iterations with continue

The continue statement skips the rest of the current iteration and moves to the next:

This skips printing 2.

# Using continue to skip iterations
for i in range(5):
    if i == 2:
        continue
    print(i)

Nested Loops

A loop inside another loop is called a nested loop. For example:

# Example of nested loops
for i in range(3):
    for j in range(2):
        print(f"i = {i}, j = {j}")

Common Mistakes with Loops

Here are some common mistakes to avoid:

• Forgetting to update the loop variable in a while loop (causing an infinite loop).
• Misusing break and continue statements.
• Incorrect indentation in nested loops.

What Did We Learn?

In this lesson, you learned:

• The basics of for and while loops.
• How to use break and continue to control loop behavior.
• How to create and use nested loops.

Great job! Let’s move on to the next topic.