QUEUES

QUEUES

• A queue is a linear data structure similar to a line in a store
• Follows FIFO (First In First Out)
• New elements are inserted at the rear
• Elements are removed from the front
• Both ends are used — front for deletion and rear for insertion

FEATURES OF QUEUE

• Linear structure
• Operates on FIFO principle
• Maintains two pointers: front → points to first element, rear → points to last element
• Overflow occurs when queue is full
• Underflow occurs when queue is empty

TYPES OF QUEUES

• Simple Queue → standard FIFO structure
• Circular Queue → connects rear to front to reuse empty space
• Priority Queue → elements served by priority rather than order

IMPLEMENTATION

• Can be implemented using arrays or linked lists
• Array implementation uses static memory
• Linked list implementation uses dynamic memory
• Head pointer (front) marks the start of the queue
• Tail pointer (rear) marks the end of the queue

BASIC OPERATIONS

• enqueue() → adds (stores) an item at the rear
• dequeue() → removes (accesses) an item from the front
• peek() → returns the front element without removing it
• isFull() → checks if queue is full
• isEmpty() → checks if queue is empty

ENQUEUE PROCESS

• Check if queue is full
• If full → return Overflow
• If not full → increment rear pointer
• Insert data at position pointed to by rear
• Return success

DEQUEUE PROCESS

• Check if queue is empty
• If empty → return Underflow
• If not empty → access data at front
• Increment front pointer to next position
• Return success

DECLARATION VARIABLES

• queue[MAX] → defines maximum capacity
• front → index of first element
• rear → index of last element
• MAX → constant for queue size

CHARACTERISTICS

• Insertion always occurs at rear
• Deletion always occurs at front
• Traversal happens from front to rear
• Queue size is limited in static implementation

ADVANTAGES

• Maintains order of processing
• Useful for scheduling and buffering

DISADVANTAGES

• Static queues waste memory after repeated insertions and deletions
• Access limited to front and rear

If you are still unsure about how queues work, please watch these videos:

• Linear Queues
• Circular Queues

Remember all notes are more accurate to the CAPE syllabus than videos