congruencia (n)

#include <iostream>

using namespace std;

int main()
{
    int b, i;
    cout << "Ingresar modulo: ";
    cin >> b;
    cout << '\n';
    for(i=0; i<b; i++)
    {
        cout << "Clase del " << i << "\n\n";
        for (int j=-1; j<20; j++)
            cout << i + b * j << " ";
        cout << "\n\n";
    }
    return 0;
}