Flow Control

The collection of devices within a programming language that allow the computer to make decisions and to repeat tasks.


A Boolean expression that commences an if or while statement. If the condition evaluates to TRUE, then the code in the body of the statement will be executed. Otherwise the code will be ignored.

Index Variable

The variable in a for loop that takes on each of the values of the iterable in succession.


The vector that provides the sequence of values for the index variable in a for loop.


The process of checking user input and rejecting it—usually with helpful suggestions—if it is not of the correct form.