华为机试—替换字符串中的字母

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
char ml[]="abcdefghijklmnopqrstuvwxyza";
char mu[]="ABCDEFGHIJKLMNOPQRSTUVWXYZA";
int main(int argc, char *argv[])
{
    string s;
    while(cin>>s)
    {
        for(int i=0;i<s.size();++i)
        {
            if(isalpha(s[i])&&isupper(s[i]))
            {
                putchar(mu[s[i]-'A'+1]);
            }
            else if(isalpha(s[i])&&islower(s[i]))
                putchar(ml[s[i]-'a'+1]);
            else
                putchar(s[i]);
        }
        putchar('\n');
    }
    return 0;
}