Imperative Programming (Cambridge International A-Level Computer Science)

Imperative programming (Procedural)

How do I write imperative (procedural) code?

• High-level languages such as Python, Java, and Visual Basic support the imperative style

• Imperative code can be made more organised and readable by using structured programming principles, such as dividing code into functions and procedures

  • Before continuing, ensure you’re confident with the basics of programming logic and have a good understanding of structured programming

Imperative programming – pseudocode (no procedures or functions)

• Task: Convert a temperature to:

  • Fahrenheit from Celsius
  • Celsius from Fahrenheit
  • Kelvin from Celsius

• Rules:

  • No procedures or functions
  • Use only global variables
  • Use a top-down, sequential flow (basic imperative structure)

Imperative pseudocode

Walkthrough – What’s happening?

• All variables are declared globally
• The entire program is written as one long block
• There is no reusability (e.g. if you want to convert again, you'd have to rerun the whole thing)
• Changes to the program will likely lead to code duplication and harder maintenance

Structured (procedural) programming – pseudocode

• Goal: Rewrite the above code using procedures or functions, local variables, and modular logic

Walkthrough – what’s improved?

• Logic is divided into reusable blocks (procedures)
• Each procedure has local variables
• The program is easier to read, maintain, and extend
• Only one global variable (choice) is used for communication
• Additional features (like repeating conversions or logging) can be added more easily

Summary