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Algorithms

Pseudo-code, flowcharts and trace tables

  • 3 things to know
  • Paper 1

Overview

Pseudo-code and why programmers design in it, the flowchart symbols for decisions, inputs, outputs and subroutines, trace tables, visual inspection, and short algorithms to trace by hand.

What you need to know

Answer each one before you reveal it.

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Key term

What is output by the algorithm x ← 5, then WHILE x > 1, x ← x − 2, ENDWHILE, then OUTPUT x?

Key term

What is the purpose of the lines temp ← a, then a ← b, then b ← temp?

Key term

What is pseudo-code?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is pseudo-code?

    Model answer

    Pseudo-code is a structured, English-like way of writing an algorithm. Pseudo-code is not a real programming language, so a computer cannot run it directly.

  2. 2

    Why do programmers design algorithms in pseudo-code?

    Model answer

    Pseudo-code lets a programmer concentrate on the logic without worrying about exact syntax. The design can then be coded in any programming language.

  3. 3

    What is a flowchart?

    Model answer

    A flowchart is a diagram of an algorithm made from standard symbols. Arrows between the symbols show the order in which the steps are carried out.

  4. 4

    Which flowchart symbol represents a decision?

    Model answer

    A diamond represents a decision. The diamond has two exits, one for a true answer and one for a false answer.

  5. 5

    Which flowchart symbol represents an input or an output?

    Model answer

    A parallelogram represents an input or an output. An example is reading a number typed by the user.

  6. 6

    What do a rounded rectangle and a plain rectangle show in a flowchart?

    Model answer

    A rounded rectangle, called a terminal, marks the start or the end. A plain rectangle shows a process such as a calculation.

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AThe algorithm outputs 1.
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