Fill an array of spiral

spiral.c

int main (int   argc, char *argv[])
{
    int i;
    int j;

    int n=2;
    int size = 2*n+1;
    int (*data)[size] = malloc(sizeof(int[size][size]));

    memset(data, 0, sizeof(int[size][size]));

    int num = 0;

    i = j = n;

    for (int offset=1; offset<=size; offset++)
    {
        int sign = (offset % 2)?-1:1;

        for(int di=1; di<= offset; di++)
        {
            i += sign;
            if(i<0)
                goto exit_;
            data[i][j] = ++num;
            printf ("data[%i,%i]=%i\n", i, j, num);
        }

        for(int dj=1; dj<= offset; dj++)
        {
            j += sign;
            if(j<0)
                goto exit_;
            data[i][j] = ++num;
            printf ("data[%i,%i]=%i\n", i, j, num);
        }
    }

exit_:
    ;
    for(i=0;i<size;i++)
    {
        for(j=0;j<size;j++)
            printf("%3i ", data[i][j]);

        printf("\n");
    }

    free(data);
}