visual c++ new outmost representation (can't possess functions)

this unequivocally simple problem that's frustrating me during moment. let's contend within unparalleled solution, i have twin projects. let's initial digest simplemath. header record "add.h"

int add(int i, int j)

and doing "add.cpp" has

int add(int i, int j) {
  relapse i+j;
}

now let's contend second digest i wish supplement function. however, code:

#include "..\simplemath\add.h"

int main() {

    add(1, 2);

}

results "unresolved outmost symbol". i second way "know" tangible doing .cpp file. side note formula regretful i indeed program.