设计规则：假设有一个字符串为“ABCDE”, 每按下一次任意键(响应WM_KEYDOWN消息)，该字符串就往前移动一格，当字符串的第一个字符碰到窗口的用户区域的边界时，该字符串就反方向移动。字符串每移动一格，颜色将随机地发生变化。-Design rules: Suppose there is a string " ABCDE" , every time you press any key (response WM_KEYDOWN messages), the string is moving forward on a grid, when a character string of the first window of the user across the boundary region , the string would move in opposite directions. Every move a string grid, the color will change randomly.