const char numbers[17] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

int getIndexOf(char a)
{
    for (int i = 0; i < strlen(numbers); i++)
    {
        if (numbers[i] == a)
            return i;
    }
    return -1;
}

string convertNumber(string number, int src, int trg)
{
    string result = "";
    int worknum = 0;
    for (int i = 0; i < number.length(); i++)
    {
        int x = getIndexOf(number[i]);
        worknum = worknum * src + x;
    }

    while (worknum)
    {
        result = numbers[worknum % trg] + result;
        worknum = worknum / trg;
    }
    return result;
}