The 'While Loop' Easy Explanation

What is a While loop?

A while loop is a control flow statement that allows code to be executed repeatedly based on a given boolean condition. The while loop can be thought of as a repeating if statement.

The while construct consists of a block of code and a condition/expression. The condition/expression is evaluated, and if the condition/expression is true, the code within the block is executed. This repeats until the condition/expression becomes false. Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre-test loop.

What they do is simply do a test like an if-statement, but instead of running the code block once, they jump back to the "top" where the while is, and repeat. A while-loop runs until the expression is False.

What does the while loop do?

A "While" Loop is used to repeat a specific block of code an unknown number of times, until a condition is met. For example, if we want to ask a user for a number between 1 and 10, we don't know how many times the user may enter a larger number, so we keep asking "while the number is not between 1 and 10".
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For example, say we want to know how many times a given number can be divided by 2 before it is less than or equal to 1. If we know a specific number, such as 32, we can say 5 times, but for a given symbolic variable "NUMBER" which represents any number in the world, how many times is not known a priori (before hand). In this case, we could use a while loop to determine that answer:
The "pseudocode" for such an algorithm is: while the number is bigger than one keep dividing it by two. additionally, keep a count of how many times we do the division.

Therefore, the while loop;

1. Like all loops, "while loops" execute blocks of code over and over again.
2. The advantage to a while loop is that it will go (repeat) as often as necessary to accomplish its goal.

Worked example

Here is a mathlab example that can find the factorials of 10. This means 10x9x8x7x6x5x4x3x2x1

​n = 10;
f = n;
while n > 1
    n = n-1;
    f = f*n;
end
disp(['n! = ' num2str(f)])

Solution

n! = 3628800

Pseudocode

​Let n be 10
f is equal to n
while n is greater than 1
the new value of n is the old value of n less 1
new value of f is a product of the old value of f and the new value of n
endwhile
print factorial

Flowchart Extract