Circular is a Queue in which the elements are arranged in a circular manner i.e. after the last element the first element comes. Instead of considering a Queue simply as linear, the blocks can be treated to frame a circle and can be felt after the last block there comes the first block. So after index N, 1 is considered as the next index and operations are done accordingly. Circular array is used to implement the circular queue. Circular array is similar to linear array and the only difference is after index N, 1 is treated as the next index.
Here in the above representation after the last index N, there comes 1 as the next index. Only here is the difference between the linear array and circular array exits.
When addition of items is done in circular queue, another condition is tested. If REAR=N then REAR is set equal to 1 and insertion is done at REAR otherwise REAR is set equal to REAR+1 andinsertion is done. In this case the overflow occurs when FRONT=1 and REAR=N. The overflow also occurs when FRONT=REAR+1. So in circular queue, the queue is said to be full if FRONT=REAR+1 or FRONT=1 and REAR=N.
Similarly while doing deletion, when FRONT=N, FRONT is set equal to 1 after deletion. When FRONT=REAR then there is a single element in the Queue. In that case when deletion is done both FRONT and REAR are set equal to 0. While doing deletion underflow occurs when FRONT=0.
Only the above mentioned changes are kept in mind while implementing the Circular Queue using one-dimensional array. The remaining part of the algorithms is same as Linear Queue.