Variables & Constants | Computer for GCSE/IGCSE - Year 11 PDF Download

Introduction

• Variables and constants store individual pieces of data in a program, accessible through their identifiers. 
• Variables are mutable and can be altered during program execution, whereas constants retain their values throughout.

Declaring Variables and Constants

• Variables are defined by specifying a data type, a name, and optionally a value.
• Constants are declared using the 'const' keyword along with a name and a value.
• When naming variables, adhere to specific rules across programming languages:
  • Names must start with a letter.
  • Names should not include spaces.
  • Variables can consist of letters, numbers, underscores (_), or dollar signs ($).
  • Avoid using reserved words like 'if', 'while', or 'for' as variable names.
• Examples of data types encompass integers, floats, Booleans, and strings.

Examples in Different Programming Languages

• Examples in Pseudocode:

  • Declare a variable named 'score' with an initial value of 10
    score ← 10
  • Declare a constant named 'PI' with a value of 3.14
    const PI ← 3.14

• Examples in Python:

  • Declare a variable named 'score' with a value of 10 using 'score = 10'
    score = 10
  • Declare a constant named 'PI' with a value of 3.14 using 'PI = 3.14'
    PI = 3.14

• Examples in Java:

  • Declare a variable named 'score' with a value of 10 using 'int score = 10;'
    int score = 10;
  • Declare a constant named 'PI' with a value of 3.14 using 'final double PI = 3.14;'
    final double PI = 3.14;

• Examples in Visual Basic:

  • Declare a variable named 'score' with a value of 10 using 'Dim score As Integer = 10'
    Dim score As Integer = 10
  • Declare a constant named 'PI' with a value of 3.14 using 'Const PI As Double = 3.14'
    Const PI As Double = 3.14