Dobble game card generator.

dobble.c

#include <stdio.h>
#include <stdlib.h>
// Dobblo generator
// Here is a C code inspired from @karinka's answer with a different arrangement of symbols.
// https://math.stackexchange.com/questions/1303497/what-is-the-algorithm-to-generate-the-cards-in-the-game-dobble-known-as-spo
    //
    // It works for n being a prime number (2, 3, 5, 7, 11, 13, 17, ...).
    //
    // Number of symbols in a given card = n+1
    // Total number of cards = n^2 + n + 1
    // Total number of symbols = n^2 + n +1
    // Author: https://math.stackexchange.com/users/375691/urmil-parikh

#define PRINT(x) printf("%2d  ", (x)+1)
void main(int argc, char *argv[]) {
    int i, j, k, r = 0, n = 5; // n is important!
    // first card
    printf ("Card %2d:  ", ++r);
    for (i = 0; i <= n; i++) {
        PRINT (i);
    }
    printf ("\n");

    // n following cards
    for (j = 0; j < n; j++) {
        printf ("Card %2d:  ", ++r);
        PRINT (0);
        for (k = 0; k < n; k++) {
            PRINT (n+1 + n*j + k);
        }
        printf ("\n");
    }

    // n*n following cards
    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            printf ("Card %2d:  ", ++r);
            PRINT (i+1);
            for (k = 0; k < n; k++) {
                PRINT (n+1 + n*k + (i*k+j)%n); // Good for n = prime number
            }
            printf ("\n");
        }
    }
}