Data structures using C,
C Program to implement circular queue. Queue is a abstract data type, In which entities are inserted into the rear end and deleted from the front end. In circular queue is connected to end to end, i,e rear and front end are connected. Compare to normal queue, Circular queue is more advantages. Read more about C Programming Language .

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#define SIZE 5            /* Size of Circular Queue */
int CQ[SIZE], f = -1, r = -1; /* Global declarations */

CQinsert(int elem) { /* Function for Insert operation */
 if (CQfull())
  printf("nn Overflow!!!!nn");
 else {
  if (f == -1)
   f = 0;
  r = (r + 1) % SIZE;
  CQ[r] = elem;
 }
}

int CQdelete() { /* Function for Delete operation */
 int elem;
 if (CQempty()) {
  printf("nnUnderflow!!!!nn");
  return (-1);
 } else {
  elem = CQ[f];
  if (f == r) {
   f = -1;
   r = -1;
  } /* Q has only one element ? */
  else
   f = (f + 1) % SIZE;
  return (elem);
 }
}

int CQfull() { /* Function to Check Circular Queue Full */
 if ((f == r + 1) || (f == 0 && r == SIZE - 1))
  return 1;
 return 0;
}

int CQempty() { /* Function to Check Circular Queue Empty */
 if (f == -1)
  return 1;
 return 0;
}

display() { /* Function to display status of Circular Queue */
 int i;
 if (CQempty())
  printf(" n Empty Queuen");
 else {
  printf("Front[%d]->", f);
  for (i = f; i != r; i = (i + 1) % SIZE)
   printf("%d ", CQ[i]);
  printf("%d ", CQ[i]);
  printf("<-[%d]Rear", r);
 }
}

main() { /* Main Program */
 int opn, elem;
 do {
  clrscr();
  printf("n ### Circular Queue Operations ### nn");
  printf("n Press 1-Insert, 2-Delete,3-Display,4-Exitn");
  printf("n Your option ? ");
  scanf("%d", &opn);
  switch (opn) {
  case 1:
   printf("nnRead the element to be Inserted ?");
   scanf("%d", &elem);
   CQinsert(elem);
   break;
  case 2:
   elem = CQdelete();
   if (elem != -1)
    printf("nnDeleted Element is %d n", elem);
   break;
  case 3:
   printf("nnStatus of Circular Queuenn");
   display();
   break;
  case 4:
   printf("nn Terminating nn");
   break;
  default:
   printf("nnInvalid Option !!! Try Again !! nn");
   break;
  }
  printf("nnnn  Press a Key to Continue . . . ");
  getch();
 } while (opn != 4);
}

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