HELP! With strings ... check digit

[xcindiix]

Hi everyone... im using C++ Microsoft visual studio and would appreciate if you can help me out here. Ive been trying to do this the whole day ... and canttt figure it outtt PLEASEE HELPPP !! I am a total beginner so sorry if i have very stupid mistakes.

#include <iostream>
#include <cmath>
#include <string>

using namespace std;

int main()
{
    int odd = 0;
    int oddsum = 0;
    int x;
    int n=0;
    int oddx2 = 0;

    string code = "7896550100164702";

    // Reversing the code order

    code = string(code.rbegin(), code.rend());
    cout << "The reverse of your code is: " << code << endl;

** // Finding the sum of the odd positions
// First multiply each number by 2
// If the result is less than 10, then sum it
// If the result is 10 or greater, then add the two digits which make this 2 digit number, e.g. 12 = 1+2

    cout << "The Odd Positions Of This Code are as follow: " << endl;

    for(int x=1; x<code.length(); x+=2)
    {        
        cout << code.at(x) << endl;
        oddsum += code[x] - '0';
    }
    cout << "The sum of the digits in the odd position = " << oddsum << endl;
    oddx2 = oddsum*2;


    cout << oddx2;
    cout << endl;

    for(int x=1; x<code.length(); x+=2)
    {        
    ???????????????????????????????????????????
    }
**

I am very stuck at the bold part, i dont know how to write this part where i have to multiply the odd positions by 2 and decide if it is greater than 9.
I managed to sum the odd positions though that is not useful