Squawk code generation (4-digit octal identifier) in c++

Question

I'm trying to generate in my C++ project squawk codes in order to assign them to a radar target.

Squawk codes are used to identified airplanes using secondary radar, they are 4 digit octal codes (eg 7066 7067 7070...) : http://en.wikipedia.org/wiki/Transponder_(aeronautics)

I would like to have a function that generate a squawk code based on the last one given, this code is at the moment stored into an int.

I would like to have something like this:

        while (IsSquawkInUse(LAST_ASSIGNED_MODEA_VFR) && LAST_ASSIGNED_MODEA_VFR < 7070) {
        if (LAST_ASSIGNED_MODEA_VFR >= 7067) {
            break;
        }
        else {
            //increment LAST_ASSIGNED_MODEA_VFR 
        }
    }

I still haven't found anything on how to actually do that without having to generate all the existing codes and pick the next one from thoses.

I'm still new to C++ and help would be greatly appreciated.

Cordialement

Answer 1

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

int main() {
    // source number as string
    string x;
    cin >> x;
    // convert it into a number
    int y = 0;
    for (int i = 0, ilen = x.size(); i < ilen; ++i) {
        y *= 8; // it's octal
        y += x[i] - '0';
    }
    // add 1 to that number
    ++y;
    // if we have a code 7777, next should be 0000
    y = y & 07777;
    // clear string x, so that we can
    x.clear();
    // write an octal number there as string
    while (y) {
        x = char(y % 8 + '0') + x;
        y /= 8;
    }
    // output that number
    cout << x << endl;
}

Live version.