Explain where in the construction of an algorithm it would be appropriate to use a procedure

11.3 Structured Programming

Learning Objective

Explain where in the construction of an algorithm it would be appropriate to use a procedure.

Why Use Procedures?

Procedures (also called sub‑routines or functions) are blocks of code that perform a specific task and can be called from multiple points in an algorithm. They help to:

• Reduce duplication of code.
• Improve readability by giving a name to a logical operation.
• Facilitate testing and debugging of individual components.
• Allow reuse of the same logic in different algorithms.

Stages of Algorithm Construction Where Procedures Are Introduced

1. Problem Analysis

   Identify repeated or complex operations that can be isolated. For example, “convert temperature”, “search a list”, or “calculate factorial”.

2. Design – Pseudocode Drafting

   Write high‑level steps. When a step represents a self‑contained task, replace it with a procedure call placeholder.

   Example:

   Read input values
   CALL sortArray(values)
   Display sorted values
   

3. Procedure Specification

   Define the procedure’s purpose, inputs, outputs, and internal steps. This can be captured in a separate pseudocode block.

   PROCEDURE sortArray(arr)
   // implementation of sorting algorithm
   END PROCEDURE
   

4. Integration into Main Algorithm

   Insert the procedure call at the appropriate point in the main flow, ensuring that data dependencies are satisfied.

5. Testing & Debugging

   Test the procedure independently (unit testing) before testing the full algorithm (integration testing).

Typical Situations for Procedure Use

Illustrative Example

Consider an algorithm that processes student marks and assigns grades. The grading logic is used several times, so it is extracted as a procedure.

MAIN
READ numberOfStudents
FOR i FROM 1 TO numberOfStudents DO
READ studentName, mark
grade ← CALL determineGrade(mark)
OUTPUT studentName, mark, grade
END FOR
END MAIN
PROCEDURE determineGrade(m)
IF m ≥ 80 THEN RETURN 'A'
ELSE IF m ≥ 70 THEN RETURN 'B'
ELSE IF m ≥ 60 THEN RETURN 'C'
ELSE IF m ≥ 50 THEN RETURN 'D'
ELSE RETURN 'F'
END IF
END PROCEDURE

In this example, the procedure determineGrade is introduced after the repeated grading logic is identified (step 1) and is then called from the main loop (step 4).

Mathematical Representation

The decision process can be expressed as a piecewise function:

\$\$

\text{grade}(m) =

\begin{cases}

A & \text{if } m \ge 80 \\

B & \text{if } 70 \le m < 80 \\

C & \text{if } 60 \le m < 70 \\

D & \text{if } 50 \le m < 60 \\

F & \text{if } m < 50

\end{cases}

\$\$

Key Take‑aways

• Introduce a procedure when a task is logically independent and likely to be reused.
• Define the procedure early in the design phase, then replace detailed steps with a call.
• Testing procedures separately improves overall algorithm reliability.
• Well‑named procedures make pseudocode easier to read and maintain.