How to calculate the day of the week for a given date (idea)

Thank you in10se, ariels, mkb.

#include<stdio.h>

main()
{
        int y;                  /* year */
        int m;                  /* month */
        int d;                  /* date (day) */
        int newdate;            /* day of the week */

        printf("Please enter the year in question:\n");
        scanf("%d", &y);
        printf("Enter the number of the month:\n");
        scanf("%d", &m);

        if (m < 3)
                {
                        m = m + 12;
                        y = y - 1;
                }

        printf("Enter the date: \n");
        scanf("%d", &d);


        newdate = (d + (2 * m) + ((6 * (m + 1)) / 10) + y + (y / 4) - 				

(y / 100) + (y / 400) + 1) % 7;

        switch (newdate)
        {
                case 0:
                {
                        puts("The day is Sunday.");
                        break;
                }
                case 1:
                {
                        puts("The day is Monday.");
                        break;
                }
                case 2:
                {
                        puts("The day is Tuesday.");
                        break;
                }
                case 3:
                {
                        puts("The day is Wednesday.");
                        break;
                }
                case 4:
                {
                        puts("The day is Thursday.");
                        break;
                }
                case 5:
                {
                        puts("The day is Friday.");
                        break;
                }
                case 6:
                {
                        puts("The day is Saturday.");
                        break;
                }
                default:
                {
                        puts("You goofed!");
                }
        }

        return 0;
}