Linear Queue

The simplest queue implementation — elements enter at the rear and leave from the front, stored in a one-dimensional array.

How a Linear Queue Works

Key Pointers

Front — points to the first element (next to be removed)
Rear — points to the last element (most recently added)

Operations

Enqueue Add to rear

Check if the queue is full (rear = MaxSize - 1)
Increment rear pointer by 1
Place the new item at queue[rear]

Dequeue Remove from front

Check if the queue is empty (front > rear)
Retrieve item at queue[front]
Increment front pointer by 1

The Problem with Linear Queues

Once the rear pointer reaches the end of the array, no more items can be added — even if spaces at the front have been freed by dequeue operations. This wasted space is the main limitation.

Initial State (Empty Queue, Size 6)

Front = 0Rear = -1

After Enqueue(A), Enqueue(B), Enqueue(C)

Front = 0Rear = 2

After Dequeue() — returns A

Front = 1Rear = 2

—0

Index 0 is now wasted space — it cannot be reused in a linear queue.

Interactive Linear Queue Simulator

Try enqueue and dequeue operations yourself. Watch the front and rear pointers move.

Array size:

Front: 0 Rear: -1 Size: 0

Queue initialised. Front = 0, Rear = -1.

Linear Queue — Pseudocode (9618 Style)

PROCEDURE Enqueue(Queue, Rear, MaxSize, Item)
    IF Rear >= MaxSize - 1 THEN
        OUTPUT "Queue is full"
    ELSE
        Rear ← Rear + 1
        Queue[Rear] ← Item
    ENDIF
ENDPROCEDURE

FUNCTION Dequeue(Queue, Front, Rear)
    IF Front > Rear THEN
        OUTPUT "Queue is empty"
        RETURN ""
    ELSE
        Item ← Queue[Front]
        Front ← Front + 1
        RETURN Item
    ENDIF
ENDFUNCTION

FUNCTION IsEmpty(Front, Rear)
    RETURN Front > Rear
ENDFUNCTION

FUNCTION IsFull(Rear, MaxSize)
    RETURN Rear >= MaxSize - 1
ENDFUNCTION

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