Define and use a procedure

11.3 Structured Programming

Objective

Define a procedure and demonstrate how to use it correctly in a program.

What is a Procedure?

A procedure (also called a sub‑program, sub‑routine or function) is a named block of code that performs a specific task. It can be called from multiple places in a program, which promotes reuse and makes the code easier to read and maintain.

Key Characteristics

• Has a unique name.
• May accept parameters (input values).
• May return a value (if it is a function) or simply perform an action (if it is a procedure).
• Encapsulates a logical unit of work.

Procedure Syntax (Python‑like Pseudocode)

def procedure_name(parameter1, parameter2, ...):
# body of the procedure
statements
return result   # optional – omitted for a pure procedure

Calling a Procedure

To use a procedure, you call it by writing its name followed by arguments in parentheses.

procedure_name(argument1, argument2, ...)

Parameter Passing Methods

Example: Calculating the Area of a Circle

Below is a simple procedure that calculates the area of a circle given its radius.

def areaofcircle(radius):
pi = 3.14159
area = pi * radius * radius
return area
# Using the procedure
r = 5
circlearea = areaof_circle(r)
print("Area =", circle_area)

Mathematically, the calculation performed is \$A = \pi r^{2}\$ where \$A\$ is the area and \$r\$ is the radius.

Advantages of Using Procedures

1. Modularity: Breaks a large program into manageable pieces.
2. Reusability: Same code can be called from different parts of the program or even other programs.
3. Readability: Meaningful names describe what the code does, making it easier to understand.
4. Maintainability: Changes need to be made in only one place.

Common Pitfalls

• Forgetting to pass the correct number or type of arguments.
• Modifying parameters unintentionally when using call‑by‑reference.
• Creating procedures that are too large or perform unrelated tasks.
• Not returning a value when one is expected (or returning when not needed).

Practice Questions

1. Write a procedure maxofthree(a, b, c) that returns the greatest of three numbers.
2. Explain the difference between call‑by‑value and call‑by‑reference using a simple example in pseudocode.
3. Given the following code, what will be printed? Explain why.

   def increment(x):
   x = x + 1
   return x
   num = 10
   increment(num)
   print(num)
   

4. Design a procedure to convert a temperature from Celsius to Fahrenheit. Include the formula \$F = \frac{9}{5}C + 32\$ in your answer.