Day 10/100: for Loops and the range() Function

Welcome to Day 10 of the 100 Days of Python series!
Today we’ll dive into the incredibly useful for loop, and the built-in range() function — two tools that let you repeat actions and iterate over sequences efficiently.

Let’s explore how to use them and where they shine. 🧠

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📦 What You'll Learn

• What a for loop is
• How range() works
• Looping over numbers, strings, and lists
• Using break, continue, and else in loops
• Real-life use cases

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🔄 What Is a for Loop?

A for loop lets you iterate over a sequence (like a list, string, or range of numbers) and execute a block of code for each item.

Basic Syntax:

for item in sequence:
    # do something with item

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🔢 The range() Function

range() generates a sequence of numbers. It’s perfect for looping a specific number of times.

for i in range(5):
    print(i)

Output:

0
1
2
3
4

range(start, stop[, step]):

• start: where to begin (default: 0)
• stop: where to end (exclusive)
• step: increment (default: 1)

Example:

for i in range(1, 6):
    print(i)  # 1 to 5

for i in range(0, 10, 2):
    print(i)  # 0, 2, 4, 6, 8

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🔁 Looping Over Strings and Lists

You can use for to iterate through any iterable (lists, strings, tuples, etc.)

Strings:

for letter in "Python":
    print(letter)

Lists:

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(f"I like {fruit}")

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🧼 Using break and continue

break: Exit the loop early

continue: Skip to the next iteration

for num in range(10):
    if num == 5:
        break  # stops at 5
    print(num)

for num in range(10):
    if num % 2 == 0:
        continue  # skips even numbers
    print(num)

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✨ Bonus: for + else

Python allows an optional else after a for loop. It runs only if the loop completes normally (no break).

for i in range(3):
    print(i)
else:
    print("Finished loop without break.")

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🔧 Real-World Example 1: Countdown with Range

for seconds in range(5, 0, -1):
    print(seconds)
print("Go!")

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📊 Real-World Example 2: Sum of Numbers

total = 0
for num in range(1, 11):
    total += num
print("Sum is:", total)

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🧠 Real-World Example 3: Finding an Item

names = ["Alice", "Bob", "Charlie"]

search = "Bob"
for name in names:
    if name == search:
        print("Found:", name)
        break
else:
    print("Name not found.")

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🚀 Recap

Today you learned:

• How to use for loops to iterate over data
• How range() helps generate numeric sequences
• Looping over strings, lists, and more
• Using break, continue, and else with loops
• Practical examples like sum, search, and countdowns

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