A Calender Program in C

#include
#include
#include
int getNumberOfDays(int month,int year)
{
   switch(month)
   {
      case 1 : return(31);
      case 2 : if(year%4==0)
   return(29);
        else
   return(28);
      case 3 : return(31);
      case 4 : return(30);
      case 5 : return(31);
      case 6 : return(30);
      case 7 : return(31);
      case 8 : return(31);
      case 9 : return(30);
      case 10: return(31);
      case 11: return(30);
      case 12: return(31);
      default: return(-1);
   }
}
char *getName(int odd)
{
   switch(odd)
   {
      case 0 :return("Sunday");
      case 1 :return("Monday");
      case 2 :return("Tuesday");
      case 3 :return("Wednesday");
      case 4 :return("Thursday");
      case 5 :return("Friday");
      case 6 :return("Saturday");
      default:return("Error in getName() module.Invalid argument
passed");
   }
}
int getOddNumber(int day,int mon,int year)
{
   int res=0,t1,t2,y=year;
   year = year-1600;
   while(year>=100)
   {
       res=res+5;
       year=year-100;
   }
   res=(res%7);
   t1=((year-1)/4);
   t2=(year-1)-t1;
   t1=(t1*2)+t2;
   t1=(t1%7);
   res = res+t1;
   res=res%7;
   t2=0;
   for(t1=1;t12000)
     res=res+1;
   res = res%7;
   return res;
}
char *getWeek(int dd,int mm,int yy)
{
   int odd;
   if(!(mm>=1 && mm<=12))
   {
      return("Invalid month value");
   }
   if(!(dd>=1 && dd<=getNumberOfDays(mm,yy)))
   {
      return("Invalid date");
   }
   if(yy>=1600)
   {
     odd = getOddNumber(dd,mm,yy);
     odd=odd%7;
     return(getName(odd));
   }
   else
   {
      return("
Please give year more than 1600");
   }
}
void printMonth(int mon,int year,int x,int y)
{
   int nod,odd,cnt,d=1,x1=x,y1=y;
   if(!(mon>=1 && mon<=12))
   {
       printf("
INVALID MONTH");
       getch();
       return;
   }
   if(!(year>=1600))
   {
      printf("
INVALID YEAR");
      getch();
      return;
   }
   if(x<=0)
     x=wherex();
   if(y<=0)
     y=wherey();
   gotoxy(x,y);
   textcolor(RED);
   cprintf("S");
   textcolor(YELLOW);
   cprintf("   M   T   W   T   F   S");
   /*       1234567891234567891234567 */
   textcolor(7);
   cprintf("");
   y++;
   nod=getNumberOfDays(mon,year);
   odd=getOddNumber(d,mon,year);
   switch(odd)
   {
     case 0 : x=x;
       cnt=1;
       break;
     case 1 : x=x+4;
       cnt=2;
       break;
     case 2 : x=x+8;
       cnt=3;
       break;
     case 3 : x=x+12;
       cnt=4;
       break;
     case 4 : x=x+16;
       cnt=5;
       break;
     case 5 : x=x+20;
       cnt=6;
       break;
     case 6 : x=x+24;
       cnt=7;
       break;
     default : printf("

INVALID DATA FROM THE getOddNumber() 
MODULE");
        return;
   }
   gotoxy(25,25);
   gotoxy(x,y);
   printf("%02d",d);
   for(d=2;d<=nod;d++)
   {
      if(cnt%7==0)
      {
 y++;
 cnt=0;
 x=x1-4;
      }
      x = x+4;
      cnt++;
      gotoxy(x,y);
      printf("%02d",d);
   }
}
main()
{
   char ch='k';
   int dd,mm,yy;
   while(ch!='0')
   {
      clrscr();
      printf("




    1.Know the day");
      printf("
    2.Print the month");
      printf("
    0.EXIT");
      printf("

    ENTER YOUR CHOICE : ");
      flushall();
      fflush(stdin);
      ch=getche();
      clrscr();
      switch(ch)
      {
 case '1': printf("Enter date (DD MM YYYY) : ");
    scanf("%d %d %d",&dd,&mm,&yy);
    printf("Day is : %s",getWeek(dd,mm,yy));
    flushall();
    getch();
    break;
 case '2' : printf("Enter month and year (MM YYYY) : ");
     scanf("%d %d",&mm,&yy);
     printf("

");
     printMonth(mm,yy,-1,-1);
     flushall();
     getch();
     break;
 case '0' : exit(0);
      }
   }
}