#include <stdio.h>
#include <stdlib.h>

int calendar (int daynum, int startday);

int main ()
{

    int done, x, y;
    done = 0;
    x = 0;
    y = 0;

    while (done != 1)
    {
    printf("Enter number of days in month: ");
    scanf("%d", &x);

        if (x == 0)
        {    done = 1;
        }
        else if (x < 28)
        {    printf("Wrong input for the number of days.\n");
        }
        else if (x > 31)
        {    printf("Wrong input for the number of days.\n");
        }
        else
        {    printf("Enter the starting day of the week (1=Sun, 7=Sat): ");
            scanf("%d", &y);

            calendar(x, y);
        }
    }


     return 0;
}

int calendar (int daynum, int startday)
{
    int nice, n1;

    printf("Sun Mon Tue Wed Thu Fri Sat \n");

    for(n1 = startday; n1 >= 0; n1--)
    {
        printf("  ");

    }

    for(n1 = 1; n1 <= daynum; n1++)
    {
        printf("   %d", n1);
    }

    return nice;
}