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Programming

Variables, constants and data types

  • 3 things to know
  • AS Unit 1

Overview

Term variable, declaring a variable and variable and a constant.

What you need to know

Answer each one before you reveal it.

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Key term

Define the term data type.

Key term

What is the danger of relying on global variables?

Key term

Define the term variable.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define the term variable.

    Model answer

    A variable is a named storage location in memory whose contents can be changed while a program is running.

  2. 2

    What is meant by declaring a variable?

    Model answer

    Declaring a variable tells the translator its name and its data type, so that memory of the right size is reserved for it and every use of it can be checked.

  3. 3

    What happens when a value is assigned to a variable?

    Model answer

    Assignment stores the given value in the variable's memory location, replacing whatever value was held there before.

  4. 4

    Distinguish between a variable and a constant.

    Model answer

    A variable holds a value that the program is free to change as it runs, whereas a constant is given its value when the program is written and cannot be altered during execution.

  5. 5

    Give one reason for defining a constant rather than typing the same number in several places.

    Model answer

    A constant such as a rate of tax is defined in one place only, so when the rate changes a single line is edited and there is no risk of an occurrence being missed.

  6. 6

    Define the term data type.

    Model answer

    A data type states what kind of value a variable may hold, which operations may be carried out on it, and how much memory is reserved for it.

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