身份证从15位到18位的计算程序

原来以为算不出来的:

#include <iostream>
#include <stdlib.h>

using namespace std;

int main()
{
    string id_in;

lg_1:
    cout << "Input you ID No: ";
    cin >> id_in;

    if (id_in.length() != 15) {
        cout << "ID has 15 number. Input again." << endl;
        goto lg_1;
    }

    string s;
    for (int i = 0; i < 15; i++){
        s = id_in.substr(i,1);
        if ((s > "9") || (s < "0")){
            cout << "ID only has number! Input again." << endl;
            goto lg_1;
        }
    }

    cout << "Your ID No is: " << id_in.substr(0,6) << "  " << id_in.substr(6) << endl;

    id_in = id_in.substr(0,6) + "19" + id_in.substr(6);

    int wi[] = {7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2,1};
    int sum = 0;

    for(int i = 0; i < 17; i++){
        sum += atoi(id_in.substr(i,1).c_str()) * wi[i];
    }

    char r[] = {'1','0','x','9','8','7','6','5','4','3','2'};

    cout << "New ID No is:  ";
    cout << id_in << r[(sum % 11)] << endl;

    return 0;
}