程序接收用户键入的一行字符（字符个数不超过80个，该字符串用回车符结束），并按字母、数字及其他字符分类计数，然后将结果存入以letter、digit和other为名的存储单元中。-Program receives the user types a line character (the number of no more than 80 characters, the string end with a carriage return)