#include <string>
static std::string str;

str = str + char(wParam); 
::InvalidateRect(hWnd, NULL, 0); 
return 0;

case WM_PAINT: 
    hdc = BeginPaint(hWnd, &ps); 
    // TODO: 在此添加任意繪圖代碼... 
    ::TextOut(hdc, 0, 0, str.c_str(),str.length()); 
    EndPaint(hWnd, &ps); 
    break;