While loop in python - Example programs in while loop python

 The Principle of 'while' Loops

• Condition-Based Repetition: Unlike for loops that iterate over a sequence, while loops keep executing a block of code repeatedly as long as a certain condition remains true.

• Check Before Entering: The condition is evaluated before each iteration of the loop. If it's false from the beginning, the loop's body will never run.

Basic Syntax

Python

condition:
    # Code to be executed while the condition is True

Example: Countdown Timer

Python

counter = 5
while counter > 0:
    print(counter)
    counter -= 1  # Decrement the counter
print("Blastoff!")

How It Works

1. Initialization: You usually initialize a variable before the loop (like counter in the example).

2. Condition Check: The condition (counter > 0) is evaluated.

3. Loop Body: If the condition is True, the code within the loop runs.

4. Update: It's crucial to update something within the loop that affects the condition. Otherwise, your loop may run forever (an infinite loop)!

5. Back to the Top: The process repeats from step 2 until the condition becomes False.

Key Points

• Indentation: Just like for loops, the indented code block defines the body of the while loop.

• Infinite Loops: Be cautious! If the condition never becomes False, your program will get stuck in an infinite loop. Always ensure there's a way for the condition to change.

When to Use 'while' Loops

• Unknown Iterations: Use while loops when you don't know beforehand how many times you need to loop (unlike for loops, which often work with sequences of known length).

• User Input: while loops are great for handling repeated logic until the user enters a specific value to stop.

• Situational conditions: Looping based on complex or changing conditions is often well-suited to while loops.

Example: Guessing Game

Python

import random

number = random.randint(1, 10) 
guess = None

while guess != number:
    guess = int(input("Guess a number between 1 and 10: "))
    if guess > number:
        print("Too high!")
    elif guess < number:
        print("Too low!") 

print("You guessed it!")

Example 1: Factorial Calculation

Python

num = int(input("Enter a number: "))

factorial = 1
i = 1
while i <= num:
    factorial *= i
    i += 1

print(f"Factorial of {num} is: {factorial}")

Example 2: Menu-Driven Program

Python

choice = ''
while choice != 'Q':  # Loop until user enters 'Q'
    print("Menu:")
    print("1. Add numbers")
    print("2. Subtract numbers")
    print("Q. Quit")
    choice = input("Enter your choice: ").upper()

    # ... (Add logic to handle choices 1 and 2 here)

Example 3: Verifying User Input

Python

valid_input = False
while not valid_input:
    age = int(input("Enter your age: "))
    if age > 0:
        valid_input = True
    else:
        print("Invalid age. Please enter a positive number.")

Example 4: Simulating Rolling Dice

Python

import random

roll_again = 'y'

while roll_again == 'y':
    print("Rolling the dice...")
    die1 = random.randint(1, 6)
    die2 = random.randint(1, 6)
    print(f"You rolled {die1} and {die2}")

    roll_again = input("Roll again? (y/n): ").lower()