Learn Python in 30 Days - Day 5: Loops (for and while)

 Learn Python in 30 Days - Day 5: Loops (for and while)

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Welcome to Day 5! Loops are a powerful feature in Python that allow you to repeat actions or iterate through collections of data. Today, we’ll cover for and while loops, along with examples to practice.

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1. What Are Loops?

A loop is a control structure that lets you execute a block of code repeatedly based on a condition or a range of values.

Types of Loops in Python:

1. for loop - Iterates over a sequence (e.g., list, range, string).
2. while loop - Repeats as long as a condition is True.

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2. The for Loop

The for loop is used to iterate over a sequence, such as a list, range, or string.

Syntax:

for item in sequence:
    # Code to execute for each item

Example 1: Looping Through a List

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

for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

Example 2: Using range()

The range() function generates a sequence of numbers.

for i in range(5):  # Loops from 0 to 4
    print("Number:", i)

Output:

Number: 0
Number: 1
Number: 2
Number: 3
Number: 4

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3. The while Loop

The while loop continues as long as a condition is True.

Syntax:

while condition:
    # Code to execute

Example 1: Counting with while

count = 0

while count < 5:
    print("Count:", count)
    count += 1  # Increment the count

Output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

Example 2: User Input with while

password = ""

while password != "python123":
    password = input("Enter the password: ")

print("Access granted!")

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4. break and continue Statements

break Statement

Stops the loop immediately.

Example:

for i in range(10):
    if i == 5:
        break
    print(i)

Output:

0
1
2
3
4

continue Statement

Skips the current iteration and moves to the next.

Example:

for i in range(5):
    if i == 2:
        continue
    print(i)

Output:

0
1
3
4

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5. Nested Loops

A loop inside another loop.

Example:

for i in range(3):
    for j in range(2):
        print(f"Outer loop: {i}, Inner loop: {j}")

Output:

Outer loop: 0, Inner loop: 0
Outer loop: 0, Inner loop: 1
Outer loop: 1, Inner loop: 0
Outer loop: 1, Inner loop: 1
Outer loop: 2, Inner loop: 0
Outer loop: 2, Inner loop: 1

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6. Practice Tasks for Day 5

Task 1: Multiplication Table

Write a program to print the multiplication table for a given number:

num = 5

for i in range(1, 11):
    print(f"{num} x {i} = {num * i}")

Task 2: Sum of Numbers

Write a program to calculate the sum of the first 10 natural numbers:

total = 0

for i in range(1, 11):
    total += i

print("Sum:", total)

Task 3: Guess the Number

Write a program that lets the user guess a number until they get it right:

import random

number_to_guess = random.randint(1, 10)
guess = 0

while guess != number_to_guess:
    guess = int(input("Guess the number (1-10): "))
    if guess < number_to_guess:
        print("Too low!")
    elif guess > number_to_guess:
        print("Too high!")

print("Congratulations! You guessed the number.")

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7. Common Mistakes to Avoid

1. Infinite Loops:
   Ensure your loop has an exit condition; otherwise, it will run forever.

   while True:  # Avoid unless intended
       print("This is infinite!")
   

2. Off-by-One Errors:
   Be careful with the start and end points of loops (e.g., range()).

3. Misplaced break or continue:
   These statements should only be used inside loops.

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8. Pro Tips for Day 5

• Use for loops when iterating over a sequence or range.
• Use while loops when the number of iterations is not fixed.
• Add comments to complex loops to explain their purpose.

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🎯 Day 5 Goal: Practice writing programs using for and while loops. Implement tasks like multiplication tables, summing numbers, and nested loops.

Let me know when you’re ready for Day 6! 🚀