Iteration Control Structures

In iteration control structures, a statement or block is executed until the program reaches a certain state, or operations have been applied to every element of a collection. This is usually expressed with keywords such as while, repeat, for, or do..until.^[1]

The basic attribute of an iteration control structure is to be able to repeat some lines of code. The visual display of iteration creates a circular loop pattern when flowcharted, thus the word “loop” is associated with iteration control structures. Iteration can be accomplished with "test before" loops, "test after" loops, and counting loops. A question using Boolean concepts usually controls how often the loop will execute.

While Loop

count assigned zero
While count < 5
    Display "I love computers!"
    Increment count
End

Do-While Loop

count assigned five
Do
    Display "Blast off is soon!"
    Decrement count
While count > zero

Repeat-Until Loop

count assigned five
Repeat
    Display "Blast off is soon!"
    Decrement count
Until count < one

For Loop

For x starts at 0, x < 5, increment x
    Display "Are we having fun?"
End

• cnx.org: Programming Fundamentals – A Modular Structured Approach using C++