题解 | 进制转换

#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int main() {
    string str = "0123456789ABCDEF";

    string s;
    getline(cin, s);

    if (s.length() <= 2) {
        return 0;
    }

    int length = s.length();
    int num = 0, index = 0, c;

    for (int i = length - 1; i >= 2; i--) {
        c = s[i];
        if (c > 0) {
            index = str.find(toupper(c));
           
            num += index * pow(16, (length - 1 - i));
        }
    }

    cout << num << endl;

}
// 64 位输出请用 printf("%lld")