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 fowcharting. The basic form of the repeat until loop is as follows:
repeat some statements or action some statements or action some statements or action update the flag until the answer to the question becomes true
In every language that I know the question (called a test expression) is a Boolean expression. The Boolean data type has two values true and false. Let's rewrite the structure to consider this:
repeat some statements or action some statements or action some statements or action update the flag until expression becomes true
Within the repeat until control structure there are three attributes of a properly working loop. They are:
- Action or actions
- Update of the fag
- Test expression
The English phrasing is, "You repeat the action until the expression becomes true". This is looping on the false. When the test expression becomes true, 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.
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