Loops are an essential concept in programming, allowing us to execute a block of code multiple times. One type of loop is the
while loop, which continues to run until a certain condition is met. In this article, we will introduce you to
while loops and show you how to use them with conditional tests. We will also provide examples and exercises to help you understand the concept better.
What is a while loop?
while loop is a control flow statement that allows us to repeat a block of code as long as a specified condition is true. The syntax for a
while loop in Python looks like this:
while condition: # code block to be executed repeatedly
condition can be any expression evaluating to
False. As long as the
condition evaluates to
True, the code block will keep executing. Once the condition becomes
False, the loop stops.
Using conditional tests with while loops
We can use conditional tests to control the execution of a
while loop. A conditional test is an expression that evaluates to either
False. If the expression is
True, the code block associated with the loop executes. If it's
False, the loop exits.
Here's an example of how we can use a conditional test with a
while loop to count from 1 to 5:
count = 1 while count <= 5: print(count) count += 1
In this example, the
count <= 5. As long as
count is less than or equal to 5, the loop will continue to execute. Inside the loop, we print the current value of
count and then increment it by 1. When
count becomes 6, the condition becomes
False, and the loop exits.
Let's take a look at some more examples to help you understand how
while loops work with conditional tests.
Example 1 - Printing even numbers
In this example, we use a
while loop to print all even numbers from 0 to 10:
num = 0 while num <= 10: print(num) num += 2
num <= 10, which means the loop will execute as long as
num is less than or equal to 10. Inside the loop, we print the current value of
num and then increment it by 2. This ensures that we only print even numbers.
Example 2 - User input validation
We can also use
while loops to validate user input. In this example, we ask the user to enter a number between 1 and 10. If the user enters an invalid number, we keep asking until they provide a valid input:
num = 0 while num < 1 or num > 10: num = int(input("Enter a number between 1 and 10: "))
num < 1 or num > 10, which means the loop will execute as long as
num is less than 1 or greater than 10. Inside the loop, we ask the user to enter a number between 1 and 10 using the
input() function. We then convert the input to an integer using the
int() function and assign it to the variable
num. The loop keeps executing as long as the user provides an invalid input.
Now that you have a basic understanding of
while loops and conditional tests, it's time to put your knowledge into practice. Here are some exercises for you to try:
Write a program that asks the user to enter a password. Keep asking until they enter the correct password (which is "password123").
Write a program that prints the first 10 Fibonacci numbers. The Fibonacci sequence starts with 0 and 1, and each subsequent number is the sum of the two preceding ones.
Write a program that asks the user to enter a number and then prints all the factors of that number.
In this article, we introduced you to
while loops and showed you how to use them with conditional tests. We also provided examples and exercises to help you understand the concept better. Looping is an important concept in programming, and
while loops are just one way to implement it. With practice, you'll be able to write complex programs using loops with ease.