oo problem

[Daok]

Ok here is the problem in a cpp file :

#include "barreprinc.h"


void BarrePrinc::AddMenu(string sNameMenu)
{
    //Put the new menu in the vector
    vMenuList.push_back(Menu(sNameMenu));
    //Ajust the size of the menu that we have
    SetLen(GetLen() - sNameMenu.length());
}//End BarrePrinc::AddMenu

void BarrePrinc::AddSubMenu(string sNameMenu, string sNameSubMenu)
{
    for (int i = 0; i < vMenuList.size(); i++)
    {
        if (vMenuList[i].GetMenuName() == sNameMenu)
        {
            vMenuList[i].AddSubMenu(sNameSubMenu);
        }//End if
    }//End for : i


}//End BarrePrinc::AddSubMenu 

Header:

#include <string>
#include <vector>
#include "menu.h"

using namespace std;

class BarrePrinc
{
    private:
        //Hold empty space in the bar
        unsigned short int iBarLen;
        //Contain all Menu in this vector
        vector<Menu> vMenuList;
        //Change the empty space that the bar can hold
        void SetLen(unsigned short int iLen){iBarLen = iLen;}
        unsigned short int GetLen(){return iBarLen;}
    public:
        //Constructor
        BarrePrinc():iBarLen(80){};
        //Functions
        void AddMenu(string sNameMenu);
        void AddSubMenu(string sNameMenu, string sNameSubMenu);

};//End class : BarrePrinc 

Why I got that error :

Compiling...
barrePrinc.cpp
main.cpp
Linking...
barrePrinc.obj : error LNK2001: unresolved external symbol "public: void __thiscall Menu::AddSubMenu(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?AddSubMenu@Menu@@QAEXV?$basic_string@DU?$char_traits@D@s
td@@V?$allocator@D@2@@std@@@Z)
Debug/MyFirstMenuInDos.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.