---
title: 6.3 Function Definition
description: "A function definition provides the complete implementation of a function. It specifies the function's return type, name, parameters, and the statements that are executed when the function is called. A function definition must contain a function body enclosed in braces.…"
url: "https://magenta-tarsier-454184.hostingersite.com/docs/cpp-programming/functions/6-3-function-definition/"
updated: "2026-09-06"
category: C++ Programming / Functions
---

# 6.3 Function Definition

A function definition provides the complete implementation of a function. It specifies the function's return type, name, parameters, and the statements that are executed when the function is called.

A function definition must contain a function body enclosed in braces. The definition can appear before or after the code that calls the function, provided that a declaration is available before the call when required.

## Source Code

```
#include <iostream>

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

int main()
{
    int result = add(10, 20);

    std::cout << "Sum: " << result << '\n';

    return 0;
}
```

## Output

```
Sum: 30
```

## Explanation

- `int add(int a, int b)` is the function definition for `add`.
- `int` specifies that the function returns an integer value.
- `add` is the name of the function.
- `a` and `b` are the function parameters.
- The statements enclosed in `{}` form the function body.
- `return a + b;` calculates the sum and returns the result to the caller.
- `add(10, 20)` calls the function and passes `10` and `20` as arguments.
- The returned value is stored in the variable `result`.
- Because the complete function definition appears before `main()`, a separate function declaration is not required in this example.
- `return 0;` terminates the program successfully.