LRESULT CALLBACK call(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam){
    static HWND mainHwnd = 0;
    LONG hw = GetWindowLong(hwnd,GWL_ID);
    HWND parent = GetParent(hwnd);
    if(msg==WM_CREATE){
        mainHwnd=*(HWND*)((CREATESTRUCT*)lParam)->lpCreateParams;
    }
    // ...
}
 
 
int main(){
 
    //...
    parentHwnd = CreateWindowEx(0, PARENT_CLASS_NAME, L"Ventana secundaria", WS_OVERLAPPEDWINDOW, 300, 300, 800, 600, NULL, NULL, hInstance,   /** Este parametro se pasa en el evento WM_CREATE **/ &mainHwnd);
 
}

char tablero[9][9];

// Si usaste cin>>X antes, coloca esta linea:
cin.ignore();
 
string t;
getline(cin, t);