从键盘输入一系列字符（以回车符结束），并按字母、数字及其他字符分类计数，最后显示这三类的计数结果（用简化段源程序结构）。-A series of characters entered from the keyboard (with a carriage return), according to the letters, numbers and other characters differential count, the last three counting results (simplified segment source structure).