Loops: Making Programs Repeat Actions

The Power of Repetition in Programming

Loops allow programs to repeat actions efficiently. Instead of writing the same code multiple times, loops let you repeat it automatically!

Why Do We Need Loops?

Imagine you want to print "Hello" 100 times. Without loops, you'd need to write 100 separate print statements. With loops, you write it once and let the computer repeat it!

Types of Loops

1. For Loops - Counting Loops

Use when you know exactly how many times to repeat something.

// Print numbers 1 to 5
    for i = 1 to 5:
        print("Number: " + i)
        
    // Output:
    // Number: 1
    // Number: 2
    // Number: 3
    // Number: 4
    // Number: 5

2. While Loops - Condition-Based Loops

Use when you want to repeat something as long as a condition is true.

count = 1

    while count <= 3:
        print("Count is: " + count)
        count = count + 1  // Important: update the condition!
        
    // Output:
    // Count is: 1
    // Count is: 2
    // Count is: 3

Loop Components

Every loop has these parts:

• Initialization: Starting point (count = 1)
• Condition: When to keep going (count <= 3)
• Update: How to change each time (count = count + 1)
• Body: What to do each time (print statement)

Real-World Loop Examples

fruits = ["apple", "banana", "orange", "grape"]

    for each fruit in fruits:
        print("I like " + fruit)
        
    // Output:
    // I like apple
    // I like banana
    // I like orange
    // I like grape

password = ""

    while password != "secret123":
        password = input("Enter password: ")
        if password != "secret123":
            print("Wrong password, try again!")
            
    print("Access granted!")

Common Loop Patterns

1. Counting Pattern

// Count from 1 to 10
    for i = 1 to 10:
        print(i)

2. Accumulator Pattern

// Add up numbers 1 to 5
    total = 0
    for i = 1 to 5:
        total = total + i
    print("Total: " + total)  // Total: 15

3. Search Pattern

// Find a specific item
    names = ["Alice", "Bob", "Charlie", "Diana"]
    found = false

    for each name in names:
        if name == "Charlie":
            print("Found Charlie!")
            found = true
            break  // Exit the loop early

Loop Control Statements

• break: Exit the loop immediately
• continue: Skip to the next iteration

for i = 1 to 10:
        if i == 3:
            continue  // Skip 3
        if i == 7:
            break     // Stop at 7
        print(i)
        
    // Output: 1, 2, 4, 5, 6

Common Loop Mistakes

• Infinite Loops: Forgetting to update the condition
• Off-by-One Errors: Starting or ending at wrong number
• Wrong Loop Type: Using while when for would be better

When to Use Each Loop Type

• For Loop: When you know the exact number of repetitions
• While Loop: When you repeat based on a condition
• For-Each Loop: When processing items in a list