This C program implements a 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 the appropriate queue function based on the user's choice and displays messages for the queue status and operations.

1. /* @author: Er. Ganesh Ram Suwal*/
#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(" 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(rear == MAX-1)
{
printf("n*********************************************************n");
printf(" Queue overflow");
printf("n*********************************************************n");
}

2. else
{
printf("Enter data : ");
scanf("%d",&data);
if(front == -1)
{
front = 0;
}
rear = rear + 1;
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;
}
printf("Dequeue element = %d",data);
}
printf("n*********************************************************n");
}
void display()
{
printf("n*********************************************************n");
if(front == -1)
{
printf("No data in the queuen");

3. printf("f = %d, r=%d",front,rear);
}
else
{
for(i = front;i<=rear; i++)
{
printf("%d(f=%d,r=%d) ",QUEUE[i],front,rear);
}
}
printf("n*********************************************************n");
}