Enqueue Operation

Queues maintain two data pointers, front and rear. Therefore, its operations are comparatively difficult to implement than that of stacks.

The following steps should be taken to enqueue (insert) data into a queue −

  • Step 1 − Check if the queue is full.

  • Step 2 − If the queue is full, produce overflow error and exit.

  • Step 3 − If the queue is not full, increment rear pointer to point the next empty space.

  • Step 4 − Add data element to the queue location, where the rear is pointing.

  • Step 5 − return success.

Insert Operation

Sometimes, we also check to see if a queue is initialized or not, to handle any unforeseen situations.

Algorithm for enqueue operation

procedure enqueue(data)      
   
   if queue is full
      return overflow
   endif
   
   rear ← rear + 1
   queue[rear] ← data
   return true
   
end procedure

Implementation of enqueue() in C programming language −

Example

int enqueue(int data)      
   if(isfull())
      return 0;
   
   rear = rear + 1;
   queue[rear] = data;
   
   return 1;
end procedure

Dequeue Operation

Accessing data from the queue is a process of two tasks − access the data where front is pointing and remove the data after access. The following steps are taken to perform dequeue operation −

  • Step 1 − Check if the queue is empty.

  • Step 2 − If the queue is empty, produce underflow error and exit.

  • Step 3 − If the queue is not empty, access the data where front is pointing.

  • Step 4 − Increment front pointer to point to the next available data element.

  • Step 5 − Return success.

Remove Operation

Algorithm for dequeue operation

procedure dequeue
   
   if queue is empty
      return underflow
   end if

   data = queue[front]
   front ← front + 1
   return true

end procedure

Implementation of dequeue() in C programming language −

Example

int dequeue() {
   if(isempty())
      return 0;

   int data = queue[front];
   front = front + 1;

   return data;
}