4.c

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>

struct node {
    int data;
    struct node *link;
};

typedef struct node *NODE;

NODE getnode();
NODE insert_front(NODE);
NODE delete_front(NODE);
NODE insert_rear(NODE);
NODE delete_rear(NODE);
void display(NODE);

void main() {
    NODE first = NULL;
    int option;
    clrscr();
    while (1) {
        printf("\nDouble-ended queue operations\n");
        printf("1. Entry-restricted queue\n2. Exit-restricted queue\n3. Display\n4. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &option);
        switch (option) {
            case 1:
                printf("\nEntry-restricted operations\n");
                printf("1. Insert\n2. Delete from front\n3. Delete from rear\n");
                printf("Enter your choice: ");
                scanf("%d", &option);
                switch (option) {
                    case 1:
                        first = insert_rear(first);
                        getch();
                        clrscr();
                        break;
                    case 2:
                        first = delete_front(first);
                        getch();
                        clrscr();
                        break;
                    case 3:
                        first = delete_rear(first);
                        getch();
                        clrscr();
                        break;
                    default:
                        printf("Invalid choice\n");
                }
                break;
            case 2:
                printf("\nExit-restricted operations\n");
                printf("1. Delete\n2. Insert from front\n3. Insert from rear\n");
                printf("Enter your choice: ");
                scanf("%d", &option);
                switch (option) {
                    case 1:
                        first = delete_front(first);
                        getch();
                        clrscr();
                        break;
                    case 2:
                        first = insert_front(first);
                        getch();
                        clrscr();
                        break;
                    case 3:
                        first = insert_rear(first);
                        getch();
                        clrscr();
                        break;
                    default:
                        printf("Invalid choice\n");
                }
                break;
            case 3:
                display(first);
                getch();
                clrscr();
                break;
            case 4:
                exit(0);
            default:
                printf("Invalid choice\n");
        }
    }
}

NODE getnode() {
    NODE temp;
    temp = (NODE)malloc(sizeof(struct node));
    return temp;
}

NODE insert_front(NODE first) {
    NODE temp;
    temp = getnode();
    printf("Enter the data: ");
    scanf("%d", &temp->data);
    temp->link = first;
    first = temp;
    printf("%d is successfully inserted\n", temp->data);
    return first;
}

NODE delete_front(NODE first) {
    NODE temp;
    if (first == NULL) {
        printf("No nodes present");
        return first;
    }
    temp = first;
    first = first->link;
    printf("%d is successfully deleted\n", temp->data);
    free(temp);
    return first;
}

NODE insert_rear(NODE first) {
    NODE temp, ptr;
    temp = getnode();
    printf("Enter the data: ");
    scanf("%d", &temp->data);
    printf("%d is successfully inserted\n", temp->data);
    temp->link = NULL;
    if (first == NULL) {
        first = temp;
        return first;
    }
    ptr = first;
    while (ptr->link != NULL)
        ptr = ptr->link;
    ptr->link = temp;
    return first;
}

NODE delete_rear(NODE first) {
    NODE ptr, prev;
    if (first == NULL) {
        printf("No nodes present\n");
        return first;
    }
    ptr = first;
    while (ptr->link != NULL) {
        prev = ptr;
        ptr = ptr->link;
    }
    printf("%d is successfully removed\n", ptr->data);
    prev->link = NULL;
    free(ptr);
    return first;
}

void display(NODE first) {
    NODE temp;
    if (first == NULL)
        printf("No nodes present\n");
    else {
        for (temp = first; temp->link != NULL; temp = temp->link)
            printf("%d=>", temp->data);
        printf("%d=>", temp->data);
    }
}