输入一个字符,如果它是大写字母,则把它变成小写字母,如果是小写字母则把它变成大写字母,其他字符不变.这个是我们大学的一个C语言作业算法!-importation of a character, if it is capital letters, put it into lowercase letters, If lowercase letters put it into capital letters, other characters unchanged. this is our univer