Sub-Procedures

Overview

Sub-procedures are smaller, self-contained units of code within a program that perform specific tasks. They are often referred to as functions or methods depending on the programming language. Sub-procedures help to break down complex problems into manageable parts, improving the readability, reusability, and maintainability of the code.

Understanding how to identify, design, and implement sub-procedures is essential for writing efficient and organised programs.

What are Sub-Procedures?

Definition: A sub-procedure is a reusable block of code that performs a specific task within a larger program.
Types of Sub-Procedures:
- Functions: Return a value after execution.
- Procedures/Methods: Perform a task but do not necessarily return a value.

Purpose of Sub-Procedures

Modularity: Breaks the program into smaller, manageable sections.
Reusability: Allows code to be reused in multiple places.
Readability: Makes the main program easier to understand by delegating tasks.
Ease of Maintenance: Simplifies debugging and updating since changes can be made in one place.

Identifying Sub-Procedures in a Problem

To identify sub-procedures:

Analyse the Problem: Break down the problem into smaller tasks or steps.
Identify Repeated Tasks: Tasks that occur multiple times can be extracted as sub-procedures.
Look for Logical Groupings: Group related tasks together.
Define Input and Output: Determine what data the sub-procedure needs to work on (inputs) and what it should return or affect (outputs).

Example Scenarios

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Scenario 1: Online Shopping System

Problem: Implement an online shopping cart.
Identified Sub-Procedures:

addToCart(item, quantity): Adds an item to the shopping cart.
calculateTotal(cart): Calculates the total cost of items in the cart.
applyDiscount(cart, discountCode): Applies a discount to the total.
checkout(cart, paymentDetails): Processes the payment.

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Scenario 2: Student Grading System

Problem: Develop a program to calculate and display student grades.
Identified Sub-Procedures:

inputGrades(): Collects grades from the user.
calculateAverage(grades): Computes the average grade.
determineGrade(average): Determines the final grade based on the average.
displayResults(grade): Displays the student's final grade.

Writing Sub-Procedures

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Pseudocode Example: Student Grading System

PROCEDURE inputGrades()
    DECLARE grades AS ARRAY
    FOR i = 1 TO 5
        OUTPUT "Enter grade:"
        INPUT grade
        APPEND grade TO grades
    ENDFOR
    RETURN grades
ENDPROCEDURE

PROCEDURE calculateAverage(grades)
    DECLARE total AS INTEGER = 0
    FOR EACH grade IN grades
        total = total + grade
    ENDFOR
    RETURN total / LENGTH(grades)
ENDPROCEDURE

PROCEDURE determineGrade(average)
    IF average >= 70 THEN
        RETURN "A"
    ELSEIF average >= 60 THEN
        RETURN "B"
    ELSEIF average >= 50 THEN
        RETURN "C"
    ELSE
        RETURN "F"
    ENDIF
ENDPROCEDURE

PROCEDURE displayResults(grade)
    OUTPUT "Final Grade: ", grade
ENDPROCEDURE

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Flowchart Example: calculateAverage(grades)

Start.
Initialise total to 0.
Loop through each grade in grades.
Add grade to total.
After the loop, calculate average = total / number of grades.
Return average.
End.

Using Parameters in Sub-Procedures

Parameters are used to pass data into sub-procedures, making them more flexible and reusable.

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Example: In the procedure calculateAverage(grades), grades is a parameter that allows the procedure to work with any set of grades.

Structure Diagrams

A structure diagram visually represents the relationship between sub-procedures in a program. It shows the hierarchical organisation of tasks.

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Example: Structure Diagram for Student Grading System

Main Program
 ├── inputGrades()
 ├── calculateAverage(grades)
 ├── determineGrade(average)
 └── displayResults(grade)

Benefits of Sub-Procedures

Improved Modularity: Each sub-procedure focuses on a single task, simplifying program design.
Code Reusability: Sub-procedures can be used in different parts of the program or other projects.
Simplified Debugging: Errors can be isolated within specific sub-procedures.
Ease of Testing: Individual sub-procedures can be tested independently.

Note Summary

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Common Mistakes

Overcomplicating Sub-Procedures: Each sub-procedure should perform a single, well-defined task.
Incorrect Use of Parameters: Failing to pass the correct data or using too many parameters can lead to confusion and errors.
Poor Naming Conventions: Sub-procedure names should reflect their purpose.

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Key Takeaways

Sub-procedures help break down complex problems into manageable tasks, improving code readability, reusability, and maintainability.
They can be represented using pseudocode, flowcharts, or structure diagrams.
Proper use of parameters enhances the flexibility and utility of sub-procedures.
Effective design and implementation of sub-procedures lead to more organised and efficient programs.

Sub-Procedures Simplified Revision Notes for A-Level OCR Computer Science

Sub-Procedures

Overview

What are Sub-Procedures?

Purpose of Sub-Procedures

Identifying Sub-Procedures in a Problem

Example Scenarios

Writing Sub-Procedures

Using Parameters in Sub-Procedures

Structure Diagrams

Benefits of Sub-Procedures

Note Summary

Common Mistakes

Key Takeaways

500K+ Students Use These Powerful Tools to Master Sub-Procedures For their A-Level Exams.

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