In programming, we have 4 ways of defining a function and they are :-

1. Takes something and returns something.
2. Takes something and returns nothing.
3. Takes nothing and returns something.
4. Takes nothing and returns nothing.

A class in C++ can have all the 4 above mentioned types of member functions as per requirement.

Syntax :

// Function Declaration - takes nothing and returns nothing

void funtion1();

// Function Declaration - takes nothing and returns something

int funtion2();

// Function Declaration - takes something and returns nothing

void funtion3(int a, int b);

// Function Declaration - takes something and returns something

int funtion4(int a, int b);

---

Example :

// Simple Function Types Example Program in C++
// Function Example

#include <iostream>

using namespace std;

void funtion1(); // Function Declaration - takes nothing and returns nothing

int funtion2(); // Function Declaration - takes nothing and returns something

void funtion3(int a, int b);

int funtion4(int a, int b); // Function Declaration - takes something and return something

int main() {
    int x, y;

    cout << "Simple Function Types Example Program in C++ \n";

    // Function Call - takes nothing and returns nothing
    funtion1();

    // Function Call - takes nothing and return something
    x = funtion2();

    cout << "\nReturnValue: " << x;

    // Function Call - takes nothing and returns nothing
    funtion3(10,20);

    // Function Call - takes nothing and return something
    y = funtion4(100, 200);

    cout << "\nAddition: " << y;

    return 0;
}

void funtion1() // Function Definition - takes nothing and returns nothing
{
    cout << "\nIt's simple function definition";
}

int funtion2() // Function Definition - takes nothing and return something
{
    int c = 1000;
    return c;
}

void funtion3(int a, int b) // Function Definition - takes something and returns nothing
{
    int c;
    c = a + b;
    cout << "\nAddition: " << c;
}

int funtion4(int a, int b) // Function Definition - takes something and return something
{
    int c;
    c = a + b;
    return c;
}

Output :

Simple Function Types Example Program in C++
It's simple function definition
Return Value: 1000
Addition: 30
Addition: 300