Module 6: Loops

In this module, we will learn about loops. Loops are used to run a block of code multiple times. This saves us from writing duplicate code.

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6.1 Why Loops?

Problem: You want to print your name on the screen 100 times.

• Without Loops: You have to write print("Sai") 100 times.
• With Loops: You can do it in just 2 lines of code.

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6.2 The for Loop

A for loop is used to iterate over a sequence (like a list, a string, or a range of numbers).

Using the range() Function:

The range(start, stop, step) function generates a sequence of numbers.

# Print numbers from 1 to 5
for i in range(1, 6):
    print(f"Number is {i}")

Looping Through a String:

name = "PYTHON"
for char in name:
    print(char)
# Output: Prints P, Y, T, H, O, N on separate lines

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6.3 The while Loop

A while loop runs as long as a specified condition remains True.

Example:

count = 1
while count <= 5:
    print(f"Count is {count}")
    count += 1 # Updates the count so the loop can stop eventually

:::danger Infinite Loop Warning If you forget to update the loop variable (like count += 1), the condition remains True forever. This creates an Infinite Loop that never stops. Press Ctrl + C in the terminal to force-stop it. :::

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6.4 The break Statement

The break statement is used to stop and exit the loop immediately, even if the loop condition is still True.

for i in range(1, 10):
    if i == 5:
        break # Exits the loop when i becomes 5
    print(i)
# Output: 1, 2, 3, 4

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6.5 The continue Statement

The continue statement skips the rest of the code in the current iteration and jumps directly to the next cycle of the loop.

for i in range(1, 6):
    if i == 3:
        continue # Skips printing 3 and moves to the next iteration
    print(i)
# Output: 1, 2, 4, 5

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6.6 The pass Statement

In Python, writing an empty loop or condition causes an error. We use the pass statement as a placeholder to do nothing and avoid errors.

for i in range(1, 5):
    if i == 2:
        pass # Placeholder for future logic
    print(i)

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6.7 Nested Loops

Writing a loop inside another loop is called a Nested Loop.

Pattern Printing Example:

# Prints a grid of stars
for i in range(1, 4):     # Outer loop (controls rows)
    for j in range(1, 4): # Inner loop (controls columns)
        print("*", end=" ")
    print() # Prints a new line after each row

Output:

* * * 
* * * 
* * * 

:::tip Think About It Every time the outer loop runs once, the inner loop runs completely (3 times). Practicing nested loops is a great way to improve your logic skills! :::