Circular Queue using Array in C Programming

#include< stdio.h>
#include< conio.h>
#define MAX 3
#define NULL -1
void main()
{
 int Q[MAX],i,j,f=NULL,r=NULL,val,ch,item;
 clrscr();
 while(1)
 {
  printf("\n1.Insert \n2.Delete \n3.Display \n4.Exit");
  printf("\n Enter Your choice:");
  scanf("%d",&val);
  switch(val)
  {
   case 1:
    if((f==0 && r==(MAX-1))||(f==r+1))
     printf("\nCircular Queue Overflow.");
    else
    {
     if(r==MAX-1)
      r=0;
     else
      r++;
     printf("\n Enter value for circular queue:");
     scanf("%d",&item);
     Q[r]=item;

     if(f==NULL)
      f=0;

             }
    break;

   case 2:
    if(f==NULL)
     printf("\n circular queue is empty.");
    else
    {
     printf("\n Deleted element is :%d",Q[f]);

     if(f==r)
      f=r=NULL;
     else if(f==(MAX-1))
      f=0;
     else
      f++;
    }
    break;
   case 3:
    if(f==NULL)
     printf("\n Circular queue is empty.");
    else
    {
     if(f<=r)
     {
      for(i=f;i<=r;i++)
         printf("\t  %d",Q[i]);
     }
     if(f>r)
     {
      for(i=f;i<=MAX-1;i++)
       printf("\t %d",Q[i]);
      for(i=0;i<=r;i++)
       printf("\t %d",Q[i]);
     }
    }
    break;
   case 4:
    exit(0);
  }
 }
getch();
}

OUTPUT

1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:2

 circular queue is empty.
1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:1

 Enter value for circular queue:11

1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:1
 
 Enter value for circular queue:22

1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:1

 Enter value for circular queue:33

1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:3
          11      22      33
1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:1

Circular Queue Overflow.
1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:2

 Deleted element is :11
1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:1

 Enter value for circular queue:44

1.Insert
2.Delete
3.Display
4.Exit
 Enter Your choice:3
         22      33      44