Dev - C++ - Alguien encuentra el error

#include <iostream>

#include <cmath>

using namespace std;

int main() {

    int Num ,C = 0;

    cout << "Numero?" << endl;

    cin >> Num;

    cout << C << "  " << Num << endl;

    while (Num >= 0) {

        C++;

        Num = Num / 10;

    }

    cout << "El numero de cifras es " << C << endl;

}

while (Num >= 0) {

while (Num > 0) {

Num = Num / 10;

Num /= 10;