Circular Queue

  


Algorithm:Circular Queue Operations


Let us consider a circular queue,CQ with front side and rear side.
Element will be inserted in rear side and will be deleted from front side.
If  rear is in the last position and front is in the middle position and 
there is any space in CQ then the item wlii be inserted in the 1st
position.This algorithm helps us to perform insertion and deletion operation
in the queue,CQ.

Initially,
	  front=rear=-1;

Qinsert(CQ[1..N),front,rear,item)
{
  if(front=(rear+1)%N)                     //checks if the Queue is full
  {
   print "Queue full"
  }
  else
  {
    rear=(rear+1)%N
    CQ[rear]=item                  //element is inserted in rear side
    if(front=-1)                    //if front is -1 then front is 
    {                                 initialized to 0
      front=0
    }
  }
}
	
Qdelete(CQ[1..N),front,rear)
{
 if(front=-1 and rear=-1)         //checks if the Queue is empty
 {
  print "Queue empty"
 }
 else
 {
   item=CQ[front]                  
   if(front=rear)              //if front and rear is equal then they 
   {                             both are initialized to -1
     front=-1
     rear=-1
   }
   else
   {
     front=(front+1)%N          //front is incremented and the element 
   }                              in front deleted
 }
 return item
}



show(CQ[1..N),front,rear)
{
  if(front=-1  and  rear=-1)       //checks if the Queue is empty
  {
    print "Queue empty"
  }
  else
  {
    for(i=front  to  rear)
    {
      print "CQ[i]"              //elements are printed one by one from front to rear
    }
  }
}


C Program For Circular Queue

Source Code:

#include<stdio.h>
#include<stdlib.h>
#include<math.h>

int Q[5],f=-1,r=-1;
void CQinsert(int item)
{
 if(f==(r+1)%5)
 {
  printf("\nQueue full.");
 }
 else
 {
  r=(r+1)%5;
  Q[r]=item;
  if(f==-1)
  {
   f=0;
  }
 }
}

int CQdelete()
{
 int item;
 if(f==-1)
 {
  printf("\nQueue empty.");
 }
 else
 {
   item=Q[f];
  if(f==r)
  {
   f=-1;
   r=-1;
  }
  else
  {
  f=(f+1)%5;
  }
 }
 return item;
}

void show()
{
 int i=0;
 if(f==-1)
 {
   printf("\nQueue empty.");
 }
 else
 {
 printf("\nThe elements of the Queue are:");
  if(f=f && i<=r)
     printf("\t%d",Q[i]);
   else
     printf("\t_");
  }
 }
 else if(f==r)
 {
  for(i=0;i<=4;i++)
  {
   if(i==f)
     printf("\t%d",Q[i]);
   else
     printf("\t_");
   }
  }
 else
 {
 for(i=0;i<=4;i++)
 {
  if(i<=r)
    printf("\t%d",Q[i]);
  else if(i>r && i %d",item);
	    }
	    break;
     case 3:
	    show();
	    break;
     case 4:
	    exit(0);

   }
 }
}


 OUTPUT:
 1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:11

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:22

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:33

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:44

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:55

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:3

The elements of the Queue are:  11      22      33      44      55

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:66

Queue full.
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

The popped item is-> 11
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

The popped item is-> 22
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

The popped item is-> 33
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:1

Enter item:77

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:3

The elements of the Queue are:  77      _       _       44      55
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

The popped item is-> 44
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

The popped item is-> 55
1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:2

1.CQinsert  2.CQdelete  3.Show  4.Exit
Enter your choice:3

Queue empty.