In today’s video, we are going to learn about Functions, which is an important topic in O Level Computer Science 2210. Functions help us organize our programs, reduce repetition, and make code easier to understand. By the end of this video, you will clearly understand what a function is, why we use it, and how it works.

What is a Function? 
A function is a named block of code that performs a specific task. Instead of writing the same instructions again and again, we place them inside a function and call the function whenever needed.
For example, if a program needs to calculate an average many times, we can create a function that calculates the average once and reuse it.

In simple words, a function is like a machine:

• You give it input

• It processes the input

• It gives an output

Why Do We Use Functions? 
Functions are used because they:

• Reduce code repetition

• Make programs easier to read and understand

• Make programs easier to test and debug

• Allow programmers to divide a big problem into smaller manageable parts

In exams, you should remember that functions improve program structure and efficiency.

Parts of a Function
A function usually has three main parts:

1. Function Definition
   This is where the function is written and given a name.

2. Parameters
   These are the values passed into the function. Parameters are optional; some functions may not need them.

3. Return Value
   A function usually sends a value back to the main program using the keyword RETURN.

Not all functions must return a value, but in 2210 syllabus, functions are mainly used to return a result.

[Example Using Pseudocode – 1 minute 20 seconds]
Let us understand functions using a simple example in pseudocode, which is required in O Level exams.

Suppose we want a function that adds two numbers.

The function definition would be:

• The function is named AddNumbers

• It takes two parameters: Num1 and Num2

• It calculates the sum

• It returns the result

In the main program, we call the function and store the returned value in a variable.

Explain to students verbally that:

• The main program sends values to the function

• The function processes them

• The result is returned to the main program

This separation makes the program neat and professional.

Function Call 
Calling a function means using the function in the main program.
When a function is called:

• Control moves from the main program to the function

• The function executes its statements

• The function returns a value

• Control comes back to the main program

This flow is important for understanding exam questions.

[Functions vs Main Program – 30 seconds]
Always remember:

• The main program controls the flow

• Functions only run when they are called

• A function can be called multiple times in the same program

Exam Tips 
For exams:

• Use clear function names

• Match parameters and return values correctly

• Write functions before or after the main program (both are acceptable)

• Use RETURN correctly in pseudocode

That brings us to the end of today’s video on Functions for O Level Computer Science 2210. Practice writing small functions and calling them correctly, as this topic is frequently tested in exams.