Functions in C++

Imagine preparing for a school event. You don’t do everything yourself, you assign responsibilities: one person handles music, another decorates, someone prints banners.
Each helper has a clear task. When needed, you simply “call” them.

Programs work the same way.
Instead of writing long, messy code, you divide tasks into functions, small reusable blocks that do one job well.

Today, your program learns how to organize its work just like a real team.

A Simple Math Helper

You're going to build a small app with two functions:

• One function adds two numbers
• Another function prints a formatted result

Here’s the output:

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========================
   MATH HELPER
   Sum: 25
========================

You’ll learn how functions are created, called, and how they make programs cleaner and smarter.

Function Declaration and Definition

A function is a named block of code that performs a specific task.
You first declare it (tell the compiler it exists) and then define what it does.
It helps keep code organized and reusable.

Example

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int add(int a, int b); // declaration
int add(int a, int b) { return a + b; } // definition

Arguments and Return Values

Functions can take arguments (inputs) and send back return values (outputs).
Arguments help you pass information in, and return values give results back.

Example

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int add(int x, int y) {
    return x + y;
}

Here, x and y are inputs, and the sum is returned.

Scope of Variables

Scope decides where a variable can be used. Variables inside a function exist only inside that function. This keeps each part of your program protected from accidental changes.

Example

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void test() {
    int x = 10; // x exists only here
}

Pass-by-Value vs Pass-by-Reference

Pass-by-value sends a copy of the variable, changes do NOT affect the original.
Pass-by-reference sends the actual variable, changes DO affect the original.

Example

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void change(int &num) { num = 50; }

Here, the & makes the function modify the real value.

Inline Functions

An inline function is expanded where it’s called, avoiding the overhead of a normal function call. Useful for small, frequently used functions to improve performance.

Example

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inline int square(int n) { return n * n; }

Let’s Build the Math Helper

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#include <iostream>
using namespace std;

int add(int a, int b) {
    return a + b;
}

void printResult(int result) {
    cout << "========================" << endl;
    cout << "   MATH HELPER" << endl;
    cout << "   Sum: " << result << endl;
    cout << "========================" << endl;
}

int main() {
    int n1 = 10;
    int n2 = 15;

    int total = add(n1, n2);
    printResult(total);

    return 0;
}

How It Works

• add() receives two numbers and returns their sum.
• printResult() displays the formatted output.
• main() coordinates everything by calling the functions.

Your program is now organized and modular, just like professional code.

Learn Together with AI

Try prompts like:

• “Explain pass-by-reference with a simple C++ example.”
• “Create a function that multiplies three numbers.”
• “Convert my function into an inline function.”

AI can generate new versions, fix errors, or show alternative solutions instantly.

Practice Time

Write a C++ program that:

1. Creates a function multiply(int a, int b) that returns the product.
2. Creates another function display(int result) that prints:

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========================
   PRODUCT RESULT
   Result: 45
========================

1. Calls both functions from main().

Use arguments, return values, and clear function structure.

You can ask AI:

“Show me how to pass values to a function in C++.”