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Question 111

Two different versions of a subroutine designed to simulate a chemical concentration C C\,C being repeatedly halved until it falls below 0.1 are shown in the pseudocode below.

Subroutine X

SUBROUTINE decay(C)
  val ← C
  steps ← 0
  REPEAT
    val ← val / 2
    steps ← steps + 1
  UNTIL val < 0.1
  OUTPUT steps
ENDSUBROUTINE

Subroutine Y

SUBROUTINE decay(C)
  val ← C
  steps ← 0
  WHILE val >= 0.1
    val ← val / 2
    steps ← steps + 1
  ENDWHILE
  OUTPUT steps
ENDSUBROUTINE

Describe two differences in the way the loops in Subroutine X and Subroutine Y execute.

[2]
Markscheme

Programming concepts Questions

  1. GCSE
  2. /Computer Science
  3. /Programming concepts

298 exam-style questions on AQA GCSE Computer Science Programming concepts. Each one has a worked solution and a mark scheme showing where the marks go.

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