This C program implements a circular queue data structure using an array. It defines functions for enqueue, dequeue, and display operations on the queue. The main function contains a menu loop that calls these functions based on user input and allows testing the queue functionality. The enqueue function adds elements to the rear of the queue, dequeue removes from the front, and display prints out the current queue contents.

1. /*@author: Er.Ganesh Ram Suwal*/
/*Circular Queue*/
#include<stdio.h>
#include<conio.h>
#include<process.h>
#define MAX 5
int QUEUE[MAX],i,data,front = -1, rear = -1;
void enqueue();
void dequeue();
void display();
void main()
{
int choice;
clrscr();
start:
printf("n*********************************************************n");
printf("n*********************************************************n");
printf(" Queue operation ");
printf("n*********************************************************n");
printf("1:Enqueuen2:Dequeuen3:Displayn4:exitnEnter your choice:");
scanf("%d",&choice);
switch(choice)
{
case 1:enqueue();
break;
case 2:dequeue();
break;
case 3:display();
break;
case 4: exit(0);
break;
default:
printf("n*********************************************************n");
printf("Invalid Choice");
printf("n*********************************************************n");
}
goto start;
}
void enqueue()
{
if(front == (rear+1)%MAX)
{
printf("n*********************************************************n");
printf(" Queue overflow");

2. printf("n*********************************************************n");
}
else
{
printf("Enter data : ");
scanf("%d",&data);
if(front == -1)
{
front = 0;
rear = 0;
}
else
{
rear = (rear + 1)%MAX;
}
QUEUE[rear] = data;
}
}
void dequeue()
{
printf("n*********************************************************n");
if(front == -1)
{
printf(" QUEUE UNDERFLOW");
}
else
{
data = QUEUE[front];
if(rear == front)
{
rear = -1;
front = -1;
}
else
{
front = (front + 1)%MAX;
}
printf("Dequeue element = %d",data);
}
printf("n*********************************************************n");
}

3. void display()
{
printf("n*********************************************************n");
if(front == -1)
{
printf("No data in the queuen");
printf("f = %d, r=%d",front,rear);
}
else
{
if(rear>front)
{
for(i = front;i<=rear; i++)
{
printf("%d ",QUEUE[i]);
}
}
else if(rear == front)
{
printf("%d ",QUEUE[rear]);
}
else
{
for(i=front;i<=MAX-1;i++)
{
printf("%d ",QUEUE[i]);
}
for(i=0;i<=rear;i++)
{
printf("%d ",QUEUE[i]);
}
}
printf("nf = %d, r=%d",front,rear);
}
printf("n*********************************************************n");
}