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，该字符串就向Y轴移动。字符串每移动一格，颜色将随机地发生变化。-Suppose a string "ABCDE", each time you press any key once, the string move one encounter the boundary of the user area of the window when the first character of the string, the string to the Y-axismovement. The string each moving color will change randomly.