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Circular Queue Implementation

Here’s a real-world application example built on top of the Circular Queue using Linked List — demonstrating how such a structure is used in Printer Job Scheduling (a common and relatable OS-level application).

C Program: Circular Queue Implementation

Real-World Application: Printer Job Scheduling using Circular Queue (Linked List)

Concept

Modern printers handle multiple print requests in a queue.
Each print job (e.g., a document or file) is stored in a queue, and the printer processes them in order (FIFO).

When one job finishes printing, the next one automatically moves to the front — making a Circular Queue a perfect fit, as the system can continuously cycle through jobs if needed (e.g., in a multi-printer setup).

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
// Structure for a printer job node
struct Job {
    int jobId;
    char fileName[50];
    struct Job *next;
};
 
struct Job *front = NULL;
struct Job *rear = NULL;
int jobCounter = 0;
 
// Function to add a print job to the queue
void addJob(char fileName[]) {
    struct Job *newJob = (struct Job*) malloc(sizeof(struct Job));
    if (newJob == NULL) {
        printf("Memory allocation failed!\n");
        return;
    }
 
    newJob->jobId = ++jobCounter;
    strcpy(newJob->fileName, fileName);
    newJob->next = NULL;
 
    if (front == NULL) {
        front = rear = newJob;
        rear->next = front;
    } else {
        rear->next = newJob;
        rear = newJob;
        rear->next = front;
    }
 
    printf("Print Job Added: [Job ID: %d, File: %s]\n", newJob->jobId, newJob->fileName);
}
 
// Function to process (dequeue) a print job
void processJob() {
    if (front == NULL) {
        printf("No print jobs in the queue.\n");
        return;
    }
 
    struct Job *temp = front;
    printf("Processing Print Job: [Job ID: %d, File: %s]\n", temp->jobId, temp->fileName);
 
    if (front == rear) {
        front = rear = NULL;
    } else {
        front = front->next;
        rear->next = front;
    }
 
    free(temp);
}
 
// Function to view the next job in the queue
void viewNextJob() {
    if (front == NULL) {
        printf("No pending print jobs.\n");
    } else {
        printf("Next Job -> [Job ID: %d, File: %s]\n", front->jobId, front->fileName);
    }
}
 
// Function to display all jobs in the queue
void displayJobs() {
    if (front == NULL) {
        printf("No print jobs in the queue.\n");
        return;
    }
 
    struct Job *temp = front;
    printf("\n--- Print Job Queue ---\n");
    do {
        printf("Job ID: %d | File: %s\n", temp->jobId, temp->fileName);
        temp = temp->next;
    } while (temp != front);
    printf("-----------------------\n");
}
 
int main() {
    int choice;
    char fileName[50];
 
    while (1) {
        printf("\n=== Printer Job Scheduler ===\n");
        printf("1. Add Print Job\n");
        printf("2. Process Next Job\n");
        printf("3. View Next Job\n");
        printf("4. Display All Jobs\n");
        printf("5. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        getchar();  // consume newline
 
        switch (choice) {
            case 1:
                printf("Enter file name to print: ");
                fgets(fileName, sizeof(fileName), stdin);
                fileName[strcspn(fileName, "\n")] = 0;  // remove newline
                addJob(fileName);
                break;
 
            case 2:
                processJob();
                break;
 
            case 3:
                viewNextJob();
                break;
 
            case 4:
                displayJobs();
                break;
 
            case 5:
                printf("Exiting Printer Job Scheduler...\n");
                exit(0);
 
            default:
                printf("Invalid choice. Please try again.\n");
        }
    }
 
    return 0;
}

Output

 
OUTPUT :

=== Printer Job Scheduler ===
1. Add Print Job
2. Process Next Job
3. View Next Job
4. Display All Jobs
5. Exit
Enter your choice: 1
Enter file name to print: Report1.pdf
Print Job Added: [Job ID: 1, File: Report1.pdf]

Enter your choice: 1
Enter file name to print: Invoice.docx
Print Job Added: [Job ID: 2, File: Invoice.docx]

Enter your choice: 4
--- Print Job Queue ---
Job ID: 1 | File: Report1.pdf
Job ID: 2 | File: Invoice.docx
-----------------------

Enter your choice: 3
Next Job -> [Job ID: 1, File: Report1.pdf]

Enter your choice: 2
Processing Print Job: [Job ID: 1, File: Report1.pdf]

Enter your choice: 4
--- Print Job Queue ---
Job ID: 2 | File: Invoice.docx
-----------------------

Key Concepts Demonstrated

Concept	Description
Dynamic Queue	Uses Linked List for flexible job management.
Circular Connection	Rear node connects to front, allowing continuous job cycles.
Real-World Relevance	Models how print spooling and CPU scheduling queues operate.

Basics of C Programming (Introductory Programs)

Control Statements & Loops in C

Functions

Arrays

Strings

Pointers

Structures and Unions

Dynamic Memory Allocation

File Handling

Data Structures in C

Advanced C Programs

User-Defined Number Programs in C

User-Defined String Programs in C