# include <stdio.h>char fun(char *c){if (*c<='Z' && *c>='A')//满足条件：*c是大写字母*c-='A'-'a';//*c = *c + 32;经典的大小写转换return *c;}int main(void){char s[81], *p=s;//分配一个空间为81的字符数组gets(s);//输入s字符while(*p){*p = fun(p);//调用fun函数putchar(*p);//输出转换后的小写字母p++;//逐个输出}putchar('\n');return 0;}/*结果：HELLOhello请按任意键继续. . .*/
