Python – While Loops

Introduction to Python While Loops

In Python, a while loop is used to repeatedly execute a block of code as long as a specified condition is true. It allows you to automate repetitive tasks and control the flow of your program based on certain conditions.

Syntax of a While Loop

The syntax of a while loop in Python is as follows:

while condition:
    # code to be executed

The condition is evaluated before each iteration. If the condition is true, the code block inside the loop is executed. Once the condition becomes false, the loop terminates and the program continues with the next line of code after the loop.

Examples of While Loops

Example 1: Counting from 1 to 5

Let’s start with a simple example that counts from 1 to 5 using a while loop:

count = 1
while count <= 5:
    print(count)
    count += 1

In this example, the variable count is initialized to 1. The while loop continues as long as count is less than or equal to 5. Inside the loop, the current value of count is printed and then incremented by 1. The loop terminates when count becomes 6.

The output of this code will be:

1
2
3
4
5

Example 2: Sum of Even Numbers

Now let’s look at an example that calculates the sum of even numbers from 1 to 10:

sum = 0
num = 1
while num <= 10:
    if num % 2 == 0:
        sum += num
    num += 1
print("Sum of even numbers:", sum)

In this example, the variable sum is initialized to 0 and num is initialized to 1. The while loop continues as long as num is less than or equal to 10. Inside the loop, an if statement checks if num is even using the modulo operator (%). If it is, num is added to the sum variable. Finally, num is incremented by 1. The loop terminates when num becomes 11.

The output of this code will be:

Sum of even numbers: 30

Example 3: User Input Validation

While loops are also useful for validating user input. Here’s an example that asks the user for a positive number:

number = -1
while number < 0:
    number = int(input("Enter a positive number: "))
print("You entered:", number)

In this example, the variable number is initially set to -1. The while loop continues as long as number is less than 0. Inside the loop, the user is prompted to enter a positive number using the input() function. The input is converted to an integer using the int() function. If the user enters a negative number, the loop continues. Once the user enters a positive number, the loop terminates and the program displays the entered number.

Conclusion

While loops are a fundamental part of programming in Python. They allow you to repeat a block of code based on a specific condition. With the help of examples, we have explored how while loops work and how they can be used in various scenarios. Remember to ensure that your loop condition eventually becomes false to avoid infinite loops. Practice using while loops to automate repetitive tasks and make your programs more efficient.