Order of Steps in Problem Solving (OCR A Level Computer Science)

Determining the Order of Steps

• In order to begin creating subroutines to solve a problem, the overall order of steps to carry out must be identified. This is done using decomposition

What is Decomposition?

• Decomposition is the act of taking a problem and breaking it down into smaller, more understandable and more easily solved sub-problems

• Top-down design is one method of decomposing a problem

Top-down design

• Top-down design involves breaking down a problem into major tasks and breaking down these major tasks into smaller sub-tasks. Each sub-task is broken down until each can be solved using a single subroutine or module. Furthermore, each sub-task should be unable to broken down further, be easily solved and be clear

• The goal of top-down design is to structure a program into small manageable tasks. Sometimes these tasks may be delegated to other developers and may need to be coordinated on as a team. It is therefore important that everyone understands the problem and how to solve it

• The advantages of decomposing a problem into sub-problems is that each subroutine is much simpler to test and maintain, especially using unit testing. As each subroutine is self-contained and well documented it is easier to find errors in code and fixing problems as they arise. It is also convenient to reuse subroutines as necessary rather than rewriting code

• Calculating the student grades for a teachers classes should be done in the following order:

  • Step 1 - Calculate the grade for each assessment 

    • For each question, mark the question and store the value

    • Sum the value of each marked question

  • Step 2 - For each student calculate the average grade across all of their assessments

    • Add up the grade for each assessment

    • Divide by the number of assessments

    • Store the result

  • Step 3 - Repeat steps 1-2 for each class