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Engineering LibreTexts

5.1: Iteration Control Structures

  • Page ID
    10671
  • Overview

    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]

    Discussion

    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.

    Iteration (Repetition) Control Structures

    pseudocode: While

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

    pseudocode: Do While

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

    pseudocode: Repeat Until

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

    pseudocode: For

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