#include<stdio.h>

int leap(int);

void main()
{
  int d, m, y;
  int ndays, wday;
  char* wdstr;
  
  printf("Enter d, m, y:\n");
  scanf("%d %d %d", &d, &m, &y);
  ndays = daysgoneby(y) + doy(d,m,y);
  wday = dow(ndays);
  switch (wday) {
    case 0: 
      wdstr = "Sun";
      break;
    case 1: 
      wdstr = "Mon";
      break;
    case 2: 
      wdstr = "Tue";
      break;
    case 3: 
      wdstr = "Wed";
      break;
    case 4: 
      wdstr = "Thu";
      break;
    case 5: 
      wdstr = "Fri";
      break;
    case 6: 
      wdstr = "Sat";
  }
  printf("Day of the week is: %d (%s).\n", wday, wdstr);
}

int leap(int y) 
{
  ...
}

int dow(int dcount) 
{
  int offset = 2; /* 1 Jan 1800 AD is a Wed */
  return ((offset + dcount) % 7);
}

int daysgoneby(int y)
{
  ...
}

int doy(int d, int m, int y) 
{
  ...
}