P123.28

28.

#include<stdio.h>#include<string.h>#define N 100void trans(char a[],int len){int i;    for(i=0;i<len;i++){    if(a[i]<91&&a[i]>64)        a[i]=a[i]+32;        else        if(a[i]<123&&a[i]>96)        a[i]=a[i]-32;    }    printf("转化结果为:%s\n",a);}main(){char a[N];    printf("请输入一串字符:\n");    trans(a,strlen(gets(a)));    return 0;}