C/C++ :: How To Compile Two CPP Files With Header File

this is my main cpp file:

#include<iostream>
#include<conio.h>
#include "C:UsersAmitDesktopNew foldersum.h"
using namespace std;
int main() {
int a;
int b;

[Code]...

this is my 2nd cpp file add two number

#include<iostream>
#include "C:UsersAmitDesktopNew foldersum.h"
int sum(int x,int y) {
return(x+y);
}

this is my header file used in both cpp file

#ifndef SUM_H
#def SUM_H
int sum(int x,int y);
#endif

error i am getting in main cpp in devc++

[Linker error] undefined reference to `sum(int, int)'
[Linker error] undefined reference to `sum(int, int)'

in 2nd cpp file [Linker error] undefined reference to `WinMain@16' [/code]