While Loop

The first type of loop we'll look at is the while loop. Imagine you want to print numbers 1-100. That would take us a long time manually. We can make it easier using a while loop:

int number = 1;
while (number <= 100) { // While number is less than or equal to 100
    std::cout << number << std::endl; // Print number
    number = number + 1; // Increase number by 1
}

You can see that the while loop has a similar structure to the if statement.

It works as follows: after the word while comes a condition, and as long as it's true, the code block of the while loop will repeat. As a reminder, a code block is the code in curly braces {} after statements like if, else or while.

Our code will therefore perform the following steps:

1. Set the value of variable number to 1.
2. Check if number is less than or equal to 100.
3. If yes, print the value of variable number, increase its value by 1 and return to step 2.
4. If no, the program ends.

Note that if we forgot to increase number by 1 in our loop, then number would always be 1 and thus our loop would repeat infinitely. This would cause a program that doesn't respond and would probably terminate itself after a while. This is always undesirable and therefore as programmers we must be careful to avoid this error.

In C++, we can also use a shorthand notation for increasing a value by 1: number++ instead of number = number + 1.