Thread: string::operand+ usage problem (with WIN32 data types)

I'm using DevC++ as compiler and this is a Win32 program...

Code:

LRESULT CALLBACK Efendi(HWND anaPen, UINT msj,WPARAM wParam, LPARAM lParam){
        int metKrkSys;
        LPTSTR metMetin;
        HWND hMet;
        hMet = GetDlgItem( anaPen, id_met);
        switch (msj) {
               case WM_COMMAND:
                    metKrkSys = GetWindowTextLength(hMet);
                    GetWindowText( hMet, metMetin, metKrkSys+1);
                    switch (LOWORD(wParam)){
                           case id_rakam0:
                                metMetin = metMetin + "abc";
                                MessageBox( anaPen, metMetin, "KarakterSayısı", MB_OK);
                                break;            
                    }
                    break;
               case WM_CLOSE:
                    DestroyWindow(anaPen);
                    break;
               case WM_DESTROY:
                    PostQuitMessage(0);
                    break;
               default:
               return DefWindowProc(anaPen, msj, wParam, lParam);      
        }
        return 0;
}

anaPen is my main window.
hMet (id_met) is an edit control.
metMetin is the text in this edit control.
id_rakam0 is a button's id.

This program wants to do this: getting the text in the edit control, adding it "abc" string then showing in a MessageBox...

When I compile:

39 D:\Denemeler\c++\win32_winprog\HesapMakinesi\main. cpp invalid operands of types `TCHAR*' and `const char[3]' to binary `operator+'

So what's the problem exactly and what should I do?