queue implementation using array in c

Queue Data Structure

A queue is a linear Data structure which allows operations in a particular order i.e. rear or front end only. The order of queue is First In First Out (FIFO) or First Come First Serve (FCFS). A good example of the queue is any queue of consumers for a resource where the consumer that came first is served first.

The difference between stacks and queues is in removing. In a stack we remove the item the most recently added; in a queue, we remove the item the least recently added.

Queue implementation using an array

#include <stdio.h>

#define MAX_SIZE 5

int rear=-1;
int front=-1;
int QUEUE[MAX_SIZE];
void Qinsert()
{
  int data;
  if(rear==MAX_SIZE-1)
  {
   printf("\nQUEUE IS OVERFLOW(FULL): ");
   return;
  }
  else
  {
   if(rear==-1)
    front=0;

   rear=rear+1;
   printf("\nEnter data: ");
   scanf("%d",&data);
   QUEUE[rear]=data;
   return;
  }
}
void Qdelete()
{
  int i;
  if(front==-1)
  {
   printf("\nQUEUE IS UNDERFLOW(EMPTY): ");
   return;
  }
  printf("\ndelete data:%d",QUEUE[front]);
  rear=rear-1;
  for(i=0; i<=rear; i++)
  QUEUE[i]=QUEUE[i+1];

  if(rear==-1)
  front=-1;
}
void Qdisplay()
{
  int i;
  if(rear==-1)
  {
    printf("\nQUEUE IS EMPTY");
    return;
  }
  printf("\nQUEUE DATA: ");
  for(i=0; i<=rear; i++)
  printf("%d ",QUEUE[i]);
  getch();
  return;
}
int main()
{
  int option;
  while(1)
  {
   clrscr();
   printf("\n1.FOR INSERT :");
   printf("\n2.FOR DELETE :");
   printf("\n3.FOR DISPLAY: ");
   printf("\n4.FOR EXIT...:");
   scanf("%d",&option);
   switch(option)
   {
    case 1: Qinsert();
          break;
    case 2: Qdelete();
          getch();
          break;
    case 3: Qdisplay();
          break;
    case 4: return 0;

    default: printf("\ninvalid option: ");
   }
  }
}