判断是不是字母，不区分大小写

#include<iostream>
#include<cctype>
using namespace std;

int main()
{
    char s;
    while(cin >> s)
    {
        if(isalpha(s))    cout << s << " is an alphabet."  << endl;
        else cout << s << " is not an alphabet."  << endl;
    }

    return 0;
}