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Programming

Iteration: count-controlled and condition-controlled loops

  • 3 things to know
  • AS Unit 1

Overview

Count-controlled loop, condition-controlled loop and pre-conditioned and a post-conditioned loop.

What you need to know

Answer each one before you reveal it.

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Key term

What is a count-controlled loop?

Key term

Distinguish between a pre-conditioned and a post-conditioned loop.

Key term

What is an infinite loop, and give one common cause of one.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by iteration?

    Model answer

    Iteration is a construct that makes a block of statements repeat, so that the same instructions can be applied many times without being written out again.

  2. 2

    What is a count-controlled loop?

    Model answer

    A count-controlled loop repeats its body a fixed number of times, governed by a counter variable that is set to a starting value, changed on every pass and tested against a limit.

  3. 3

    Which statement normally provides a count-controlled loop?

    Model answer

    The FOR statement provides a count-controlled loop in most programming languages.

  4. 4

    What is a condition-controlled loop?

    Model answer

    A condition-controlled loop repeats its body for as long as a stated condition holds, and the number of repetitions is not known when the program is written.

  5. 5

    Distinguish between a pre-conditioned and a post-conditioned loop.

    Model answer

    A pre-conditioned loop tests its condition before the body, so the body may be skipped altogether, while a post-conditioned loop tests after the body, so the body always runs at least once.

  6. 6

    Which kind of loop suits the validation of an input, and why?

    Model answer

    A post-conditioned loop such as REPEAT UNTIL suits validation, because a value has to be entered once before it can be judged, and the loop then repeats only while the entry remains unacceptable.

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