win32编程中的问题

/*
       程序实现的是输入字符并且在窗口显示出来，按下backspace键的时候消去一个
*/
下面是主要代码
i，还有szBuffer设置为全局变量
case WM_CHAR:
            
              switch(wParam)
              {
                  case '\b':
                         i--;
                         if(i<=0)
                         i=0;
                        szBuffer[i]=' ';
                       break;
             default:                     
                        szBuffer[i]=wParam;
                        i++;
                        szBuffer[i]=0;
              }
                 break;
           case  WM_PAINT:
                 GetClientRect(hwnd,&rect);
                 hdc=BeginPaint(hwnd,&ps);
                 DrawText(hdc,szBuffer,-1,&rect,DT_LEFT);
                InvalidateRect(hwnd,&rect,false);//这一句如果不加上的话字符为什么不显示，加上之后就会闪烁，问一下有没有其他方案
                 EndPaint(hwnd,&ps);
                 return 0;