Basic Use Of Classes - Help

I seem to be getting this error:

Quote:

Converter.obj : error LNK2019: unresolved external symbol "public: double __thiscall convert::MPH2KM(double)" (?MPH2KM@convert@@QAENN@Z) referenced in function _main

fatal error LNK1120: 1 unresolved externals

**Converter.cpp**

Code:

`#include "stdafx.h"`

#include <iostream>

#include "m4th2.h"

using std::cout;

using std::cin;

int main()

{

//Variables declared, one for the choice made by the user

//the other for the value entered for converting.

int choice;

double mph;

//double pounds;

//double inches;

convert convert2;

cout << "This Is A Converter\n";

cout << "Menu:\n" << "1 - MPH To KM\n" << "2 - Pounds To Kilos\n" << "3 - Inches To CM\n";

cout << "Please Enter A Choice:\n";

cin >> choice;

if (choice == 1)

{

cout << "Please Enter The Amount Of MPH To Convert To KM:\n";

cin >> mph;

cout << convert2.MPH2KM(mph);

}

else if (choice == 2)

{

cout << "Please Enter The Amount of Pounds To Convert To Kilos\n";

}

else

{

cout << "Please Enter The Amount of Inches To Convert To CM\n";

}

return 0;

}

**m4th.cpp**

Code:

`#include "stdafx.h"`

#include "m4th2.h"

double MPH2KM(double mph)

{

double km;

double mphconv = 1;

km = mph * 1.609;

return km;

}

**m4th.h**

Code:

`#include <iostream>`

class convert

{

public:

double MPH2KM(double mph);

double P2K(double p);

double I2C(double i);

};

Can anyone help?