Page 189 - DCAP201_FUNDAMENTALS_OF_DATA_STRUCTURES

Fundamentals of Data Structures

Notes The code written above shows the enqueue operation on a queue, i.e. inserting elements to it.
Line marks the beginning of the enqueue function. Line 3 declares a variable item that will
supposedly hold the value that is to be inserted.

Notes Although we can even approach in a different way, we could have even passed the
element to be inserted as an argument to the function, well let’s proceed with our current
approach.
Line 4 is the condition for a full queue or we can say queue overflow. Logically speaking if the
value of rear is equal to MAX-1 (stating the maximum number of elements a queue can accept),
than it obviously states that the queue is full. Line 5 displays the appropriate message if the
condition is true.

Figure 11.1: Enqueue Operation on a Queue

Line 8 is the part if the queue overflow condition is false, another if condition is encountered and
it checks if the queue is empty or queue underflow. The variable queue is initially initialized as
–1 which states that the queue is empty. When the first element is inserted the queue is initialized
to zero. Hence since its time for inserting the first element, we initialize the queue as zero if the
queue is empty. Line 11 accepts the data that is to be inserted and saves it in variable item. Line
12 increments the rear variable since it has to be incremented every time we will insert an
element. We insert the element to be added on to the array queue[].

11.1.2 Dequeue Operation

This operation is used to remove an item from the queue at the front end. Now the tail count will
be decremented by one each time when an item is removed from the queue until the queue
reaches the head point.

!

Caution This operation will be performed at the front end of the queue.
The dequeue operation is shown by the dequeue function which helps to delete an element:-
1. dequeue()

2. {
3. if (front == -1 || front > rear) /* queue empty condition */
4. {

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