Implement Queue and its operation | with simple code

QUEUE :- queue as FIFO(First in First Out) data structure, which means that element inserted first will be removed first. Which is exactly how queue system works in real world. If you go to a ticket counter to buy movie tickets, and are first in the queue, then you will be the first one to get the tickets. Right? Same is the case with Queue data structure. Data inserted first, will leave the queue first.

ENQUEUE:- The process to add an element into queue is called Enqueue
DEQUEURE:- The process of removal of an element from queue is called Dequeue.

 // write a program in c  to implement a Queue 
 // and its operation

  #include <stdio.h>
  #include <stdlib.h>
  #define MAX 50
  int Q[MAX];
  int main()
  {
      int r = -1, f = -1; // r->rear, f->front
      int i, item;
      int choice;
      while (1)
      {
            printf("Choose one of these options\n");
            printf("1. Enqueue\n");
            printf("2. Dequeue\n");
            printf("3. Display\n");
            printf("4. Quit\n");
            printf("Enter your choice : ");
            scanf("%d", &choice);
            switch (choice)
            {
            case 1:
                  if (r == MAX - 1)
                        printf("Queue Overflow :\n ");
                  else
                  {
                        if (f == -1)
                              f = 0;
                        printf("Enter the element\n ");
                        scanf("%d", &item);
                        r = r + 1;
                        Q[r] = item;
                  }
                  break;
            case 2:
                  if (f == -1 || f > r)
                  {
                        printf("Queue Underflow \n");
                        return;
                  }
                  else
                  {
                        printf("Element deleted from queue is : %d\n", Q[f]);
                        f = f + 1;
                  }
                  break;

            case 3:
                  if (f == -1)
                        printf("Queue is empty \n");
                  else
                  {
                        printf("Elements in Queue is : ");
                        for (i = f; i <= r; i++)
                              printf("%d ", Q[i]);
                        printf("\n");
                  }
                  break;
            case 4:
                  exit(1);
            default:
                  printf("Wrong choice");
            }
      }
      return 0;
   }

When the above program is executed, it produces following results --

  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 1
  Enter the element
   23
  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 1
  Enter the element
   65
  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 3
  Elements in Queue is : 23 65 
  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 2
  Element deleted from queue is : 23
  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 3
  Elements in Queue is : 65 
  Choose one of these options
  1. Enqueue
  2. Dequeue
  3. Display
  4. Quit
  Enter your choice : 4