the header file is addition.h
below is header
--------------------------
#ifndef addition.h
#define addition.h

int add(int x, int y)
{
    return x + y
}
#endif // addition.h




Below is the main
--------------------------
#include <iostream>
#include "addition.h"

using namespace std;

int main()
{

    // This is like my first program ever.  Woot.
    // Hopefully this becomes ever so nostalgic as I become a master programmer!

    //Start up and welcome
    //I am quite proud of my welcome box ;)
    cout << " XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" << endl;
    cout << " X      Welcome to the Math Program          X" << endl;
    cout << " X             It will find 'C'              X" << endl;
    cout << " X              Let's Begin!                 X" << endl;
    cout << " XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" << endl;


    int x;
    int y;
    int z;
    int wish;

    cout << " What would you like to do? " << endl;              // These Determine
    cout << " Select one :" << endl;                             // the desired opetation
    cout << "   1. Addition " << endl;                           // that the user wishes to
    cout << "   2. Subtraction " << endl;                        // use.
    cout << "   3. Multiplication " << endl;
    cout << "   4. Division " << endl;
    cin >> wish;

    // The Following determines what function is being used

    if(wish == 1)                                                // For Addition, the program
    {                                                            // gets the numbers then adds them
        cout << " You chose Addition! " << endl;
        cout << "   Please enter the First Number: ";
        cin >> x;
        cout << "           Number 1 = " << x << endl;
        cout << "   Please enter the Second Number: ";
        cin >> y;
        cout << "           Number 2 = " << y << endl;



        cout << "    The sum of the two numbers is " << z << endl;

    }