MIT-Curricular/DS/C/endsem-omnibus/circq.c

#include <stdio.h>
#include <stdlib.h>
#define MAX 5

int queue[MAX];
int front = -1;
int rear = -1;

// Different from normal queue: Need to check if (rear+1)%MAX == front for full condition
int isFull() {
    if((rear + 1) % MAX == front)
        return 1;
    return 0;
}

// Different from normal queue: Both front and rear can wrap around to 0
int isEmpty() {
    if(front == -1)
        return 1;
    return 0;
}

void enqueue() {
    int item;
    if(isFull()) {
        printf("\nQueue is Full!!");
    }
    else {
        printf("\nEnter element to insert: ");
        scanf("%d", &item);
        // Different from normal queue: rear wraps around using modulo
        if(front == -1) {
            front = rear = 0;
        }
        else {
            rear = (rear + 1) % MAX;
        }
        queue[rear] = item;
        printf("\nElement inserted successfully!");
    }
}

void dequeue() {
    if(isEmpty()) {
        printf("\nQueue is Empty!!");
    }
    else {
        printf("\nDeleted element is: %d", queue[front]);
        // Different from normal queue: front wraps around using modulo
        if(front == rear) {
            front = rear = -1;
        }
        else {
            front = (front + 1) % MAX;
        }
    }
}

void display() {
    int i;
    if(isEmpty()) {
        printf("\nQueue is Empty!!");
    }
    else {
        printf("\nQueue elements are: ");
        // Different from normal queue: Need to use modulo to wrap around while displaying
        for(i = front; i != rear; i = (i + 1) % MAX) {
            printf("%d ", queue[i]);
        }
        printf("%d", queue[i]);
    }
}

int main() {
    int choice;
    while(1) {
        printf("\n\n1. Insert");
        printf("\n2. Delete");
        printf("\n3. Display");
        printf("\n4. Exit");
        printf("\nEnter your choice: ");
        scanf("%d", &choice);

        switch(choice) {
            case 1:
                enqueue();
                break;
            case 2:
                dequeue();
                break;
            case 3:
                display();
                break;
            case 4:
                exit(0);
            default:
                printf("\nInvalid choice!!");
        }
    }
    return 0;
}