Why do while

This module covers both. The concept of iteration is connected to possibly wanting to repeat an action. Like all control structures, we ask a question to control the execution of the loop. The term loop comes from the circular looping motion that occurs when using flowcharting. The basic form of the do while loop is as follows:. In most programming languages the question called a test expression is a Boolean expression.

The Boolean data type has two values — true and false. Within the do while control structure there are three attributes of a properly working loop. They are:. This is looping on the true. When the test expression is false, you stop the loop and go on with the next item in the program. Notice, because this is a test after loop the action will always happen at least once.

It is called a test after loop because the test comes after the action. It is also sometimes called a post-test loop, meaning the test is post or Latin for after the action and update. The basic form of the repeat until loop is as follows:.

Within the repeat until control structure, there are three attributes of a properly working loop. This is looping on the false.

Here's what it does. First, the statements are executed, then the condition is tested; if it is true , then the entire loop is executed again. The loop exits when the test is performed and gives a false result. This kind of loop is most often used when the test doesn't make any sense until the statements have been performed at least once.

For most purposes, the while loop is preferable. Arithmetic Assignment Comparison Logical. Boolean Values Boolean Expressions. Create References Memory Address. Create Pointers Dereferencing Modify Pointers. Report Error. Your message has been sent to W3Schools.