A queue is a linear data structure that follows the FIFO (First In First Out) principle. In this tutorial, you’ll learn how to implement a queue using a linked list in C, including enqueue, dequeue, and display operations.
Why Use Linked List for Queue?
Queues implemented using arrays have a fixed size and can lead to overflow. By using a linked list, we eliminate this limitation, allowing the queue to grow dynamically based on memory availability.
Queue Operations
| Operation | Description |
|---|---|
| ENQUEUE | Add an element at the rear of the queue |
| DEQUEUE | Remove an element from the front |
| DISPLAY | Show all elements from front to rear |
C Program: Queue Using Linked List
#include <stdio.h>
#include <stdlib.h>
// Node structure
struct Node {
int data;
struct Node* next;
};
struct Node* front = NULL;
struct Node* rear = NULL;
// ENQUEUE operation
void enqueue(int value) {
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
newNode->next = NULL;
if (rear == NULL) {
front = rear = newNode;
} else {
rear->next = newNode;
rear = newNode;
}
printf("%d enqueued to queue\n", value);
}
// DEQUEUE operation
void dequeue() {
if (front == NULL) {
printf("Queue is empty\n");
return;
}
struct Node* temp = front;
printf("%d dequeued from queue\n", front->data);
front = front->next;
free(temp);
if (front == NULL) {
rear = NULL;
}
}
// DISPLAY operation
void display() {
if (front == NULL) {
printf("Queue is empty\n");
return;
}
struct Node* temp = front;
printf("Queue elements: ");
while (temp != NULL) {
printf("%d -> ", temp->data);
temp = temp->next;
}
printf("NULL\n");
}
// Main function
int main() {
int choice, value;
do {
printf("\nMenu:\n1. Enqueue\n2. Dequeue\n3. Display\n4. Exit\n");
printf("Enter your choice: ");
scanf("%d", &choice);
switch (choice) {
case 1:
printf("Enter value to enqueue: ");
scanf("%d", &value);
enqueue(value);
break;
case 2:
dequeue();
break;
case 3:
display();
break;
case 4:
printf("Exiting...\n");
break;
default:
printf("Invalid choice. Try again.\n");
}
} while (choice != 4);
return 0;
}
Output Example
Menu:
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: 1
Enter value to enqueue: 10
10 enqueued to queue
Enter your choice: 1
Enter value to enqueue: 20
20 enqueued to queue
Enter your choice: 3
Queue elements: 10 -> 20 -> NULL
Enter your choice: 2
10 dequeued from queue
Enter your choice: 3
Queue elements: 20 -> NULL
Key Benefits of Linked List Queue
- No fixed size
- Dynamically grow and shrink
- No wasted memory
- Useful in real-time systems and process scheduling