header - LNK2019 error with functions used in main with Visual Studio 2012 C++

I receive the following error:

1>main.obj : error LNK2019: unresolved external symbol "void __cdecl
setup(void)" (?setup@@YAXXZ) referenced in function _main 1>main.obj :

error LNK2019: unresolved external symbol "void __cdecl display(void)"
(?display@@YAXXZ) referenced in function _main
1>C:\code\Project1\Debug\Project1.exe : fatal error LNK1120: 2
unresolved externals

How do i resolve this?

Here is the main class, where the functions are used:

#include "interface.h"
using namespace std;

int main(){
    setup();
    display();
    system("pause");
    return 0;
}

Here is interface.cpp

#include 
#include 
#include "interface.h"
using namespace std;
class ui{
    void setup(){
        options[0][0]="Hello";

        options[1][0]="Hello";
        options[2][0]="Hello";
        options[3][0]="Hello";
        options[4][0]="Hello";
        options[5][0]="Hello";
        options[6][0]="Hello";
        options[7][0]="Hello";
        options[8][0]="Hello";
        options[9][0]="Hello";
    }

    void changeOption(int whatOption, string whatText,
                  string prop1, string prop2, string prop3, string prop4, string prop5){
        options[whatOption][0]=whatText;
        options[whatOption][1]=prop1;
        options[whatOption][2]=prop2;
        options[whatOption][3]=prop3;
        options[whatOption][4]=prop4;
        options[whatOption][5]=prop5;
    }
    void display(){

        for(int x=0;x<9;x++){
            cout<        }
    }
};

and here is interface.h

#include 

//#include 
using namespace std;
#ifndef INTERFACE_H_INCLUDED
#define INTERFACE_H_INCLUDED
    void setup();
    extern string options[10][6];
    void changeOption(int whatOption, string whatText, string prop1, string prop2, string prop3, string prop4, string prop5);
    void display();
#endif INTERFACE_H

Answer

You declare these as global functions.

However, your implementation defines them inside of class ui{.

You can remove the class ui{ and matching closing parenthesis and it should work correctly.