题解 | #进制转换#

#include <cmath>
#include <cstdlib>
#include <iostream>
#include <math.h>
#include <ostream>
#include <sstream>
#include <string>
using namespace std;

int main() {
    // int a, b;
    // while (cin >> a >> b) { // 注意 while 处理多个 case
    //     cout << a + b << endl;
    // }
    string str, real;
    getline(cin, str);
    real = str.substr(2);
    //  cout<<real<< endl;
    int length = real.length();
    int max_pow = length - 1;
    int trans = 0, c = 0, a = 0;
    for (int i = 0; i <= max_pow; i++) {
        // cout<<real[i]*1<< endl;
        //  cout<<max_pow<< endl;
        //  cout<<pow(16,  max_pow-i)<< endl;
        //  cout<<real[i]<< endl;
        //    cout<<(int)real[i]<< endl;

        // cout<<c<< endl;
        // cout<<real[i]<< endl;
        switch (real[i]) {
            case 'a':
            case 'A':
                c = 10;
                break;
            case 'b':
            case 'B':
                c = 11;
                break;
            case 'c':
            case 'C':
                c = 12;
                break;
            case 'd':
            case 'D':
                c = 13;
                break;
            case 'e':
            case 'E':
                c = 14;
                break;
            case 'f':
            case 'F':
                c = 15;
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':

                c = (int)real[i] - 48;

                break;

            default:
                break;
        }



        // cout << "c is " << c << endl;
        // cout << "pow is " << max_pow - i << endl;

        // cout << "pow is " << pow(16,  max_pow - i) << endl;
        a = c * pow(16,  max_pow - i);
        // cout << "a is " << a << endl;
        trans += a;
        // cout << trans << endl;
        // cout<<trans<< endl;
    }
    cout << trans;

}
// 64 位输出请用 printf("%lld")