简洁易懂，可观性高的题解

#include<iostream>
using namespace std;
string s;
int a, n, q;
int main(){
    getline(cin, s);
    for(int i = 0; i < s.size(); i++){
        if(s[i] == '?'){
            break;
        }if(s[i] >= 'a' && s[i] <= 'z'){
            a++;    
        }else if(s[i] >= '0' && s[i] <= '9'){
            n++;
        }else{
            q++;
        }
    }
    cout << "Letters=" << a << endl;
    cout << "Digits=" << n << endl;
    cout << "Others=" << q;
    return 0;
}