11.3 Structured Programming: Procedures

In structured programming, procedures (also known as subroutines or functions) are fundamental building blocks that allow you to break down a large program into smaller, more manageable and reusable sections. They promote modularity, making code easier to understand, debug, and maintain.

What is a Procedure?

A procedure is a sequence of instructions that performs a specific task. It can accept input values (parameters), process those values, and optionally return a result. Procedures help avoid code repetition and improve program organization.

Why Use Procedures?

• Modularity: Breaks down complex problems into smaller, easier-to-understand parts.
• Reusability: A procedure can be called multiple times from different parts of the program, avoiding redundant code.
• Maintainability: Changes to a procedure only need to be made in one place.
• Readability: Makes code easier to read and understand.

Defining a Procedure

To define a procedure, you specify its name, the parameters it accepts (if any), and the block of code that makes up the procedure's body. The syntax for defining a procedure varies depending on the programming language, but the general concept remains the same.

Consider the following pseudocode example:

Line	Code	Description
1	procedure CalculateArea(length, width)	Defines a procedure named 'CalculateArea' that takes two parameters: 'length' and 'width'.
2	area = length * width	Calculates the area by multiplying length and width.
3	output area	Displays the calculated area.
4	end procedure	Marks the end of the procedure definition.

Calling a Procedure

To execute a procedure, you 'call' it. This involves using the procedure's name followed by parentheses containing any required arguments (values to be passed to the procedure's parameters).

Using the same pseudocode example:

Line	Code	Description
1	CalculateArea(5, 10)	Calls the 'CalculateArea' procedure with arguments 5 and 10. The procedure will calculate the area of a rectangle with length 5 and width 10.

Parameters and Arguments

Parameters: Variables declared in the procedure definition that act as placeholders for input values.

Arguments: The actual values passed to the procedure when it is called. Arguments are assigned to the corresponding parameters.

Example: A More Complex Procedure

Let's consider a procedure that calculates the volume of a cylinder:

Line	Code	Description
1	procedure CalculateCylinderVolume(radius, height)	Defines a procedure to calculate the volume of a cylinder.
2	volume = $\pi \times radius^2 \times height$	Calculates the volume using the formula.
3	output volume	Displays the calculated volume.
4	end procedure	Marks the end of the procedure definition.

To use this procedure:

Line	Code	Description
1	CalculateCylinderVolume(2, 10)	Calls the procedure with a radius of 2 and a height of 10.

This procedure demonstrates how parameters and arguments are used to pass data to the procedure and calculate the volume based on that data.