Introduction of Queue

In C or C++, queue is like a line of people whose standing for taking a ticket of movie in theater and standing in railway reservation counter. Queue is also called first-in-first-out ( FIFO) or last-in-last-out ( LILO) list. Its mean that any element added at last to the queue is remove last and first element remove first. In queue, insertion of a new element is at one end and deletion of a element at the other end. The end where the deletion of a element takes place is known as front. The end where the addition of a element takes place is known as rear. 

When we use Queue...


Advantages of Queue...





Disadvantage of Queue...




Operations on Queue...

struct qnode

{

   int value;

   struct qnode * link;

};

void add( struct qnode **,struct qnode **,  int);

int delete( struct qnode **, struct qnode ** );

int peek( struct qnode **, struct qnode ** );

void deleteallnode( struct qnode **, struct qnode ** );

int count( struct qnode * );

void display( struct qnode * );

void main()

{

   struct snode  * frontptr = NULL;

   struct snode  * rearptr = NULL;

   add( &frontptr, &rearptr, value);

   add( &frontptr, &rearptr, value);
   add( &frontptr, &rearptr, value);

   delete( &frontptr, &rearptr);

   peek( &frontptr, &rearptr );

   deleteallnode( &frontptr, &rearptr);

   count( frontptr);

   display( frontptr);

}

void add( struct qnode **front, struct qnode **rear, int value)
{
   struct qnode * temp= NULL;
   temp= ( struct qnode *) malloc( sizeof( struct qnode));
   temp-->data = value;
   temp-->link = NULL;
   if( *rear== NULL)
   {
      *front= *rear= temp;
      temp= NULL;
   }
   else
   {
      struct qnode *temp1= *rear;
      *rear= temp;
      temp1-->link= temp;
      temp= temp1= NULL;
   }
}

int delete(struct qnode ** front, struct qnode **rear)
{
   struct qnode *temp= *front;
   if( front== NULL)
   {
      cout<< "queue is empty";
   }
   if( temp-->link== NULL)
   {
      int value= temp-->data;
      *front= *rear= NULL;
      free( temp);
      temp= NULL;
   }
   else
   {
      struct qnode *temp1= *front;
      int value= temp-->data;
      temp1= temp1-->link;
      *front= temp1;
      temp-->link= NULL;
      free( temp);
      temp= temp1= NULL;
   }
   return value;
}

int peek( struct qnode **front, struct qnode **rear)
{
   struct qnode *temp= *front;
   if( temp== NULL)
   {
      cout<< "queue is empty";
      return -1;
   }
   else
   {
      int value= temp-->data;
      return value;
   }
}

void deleteallnode( struct qnode **front, struct qnode **rear )
{
   struct qnode **temp= *front;
   if( *front== NULL)
   {
      cout<< "queue is empty";
   }
   else
   {
      if( temp-->link== NULL)
     {
        *front= *rear= NULL;
        free( temp);
        temp= NULL;
     }
     else
     {
        struct qnode *temp1= temp-->link;
        while( temp!= NULL)
        {
           temp-->link= NULL;
           free( temp);
           *front= temp1;
           temp= *front;
           temp1= temp1-->link;
        }
        *front= *rear= NULL;
        free( temp);
        temp= NULL;
     }
  }
}

int count( struct qnode *frontptr)
{
   int c= 0;
   if( frontptr== NULL)
   {
      cout<< "queue is empty";
   }
   else
   {
      while( frontptr != NULL)
      {
         c++;
         frontptr= frontptr-->link;
      }
    }
    return c;
}

void display( struct qnode *frontptr)
{
   if( frontptr== NULL)

   {

      cout<< "queue is empty";

   }

   else

   {

      while( frontptr != NULL)

      {

         cout<< frontptr-->data;

         frontptr= frontptr-->link;

      }

   }

}