Linked_List

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

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

struct node *start = NULL;
struct node *create_ll(struct node *);
struct node *display(struct node *);
struct node *insert_beg(struct node *);
struct node *insert_end(struct node *);
struct node *insert_before(struct node *);
struct node *insert_after(struct node *);
struct node *delete_beg(struct node *);
struct node *delete_end(struct node *);
struct node *delete_node(struct node *);
struct node *delete_after(struct node *);
struct node *delete_list(struct node *);
struct node *sort_list(struct node *);

void main()
{
    int option;
    do
    {
        printf("\n\n *****MAIN MENU *****");
        printf("\n 1: Create a list");
        printf("\n 2: Display the list");
        printf("\n 3: Add a node at the beginning");
        printf("\n 4: Add a node at the end");
        printf("\n 5: Add a node before a given node");
        printf("\n 6: Add a node after a given node");
        printf("\n 7: Delete a node from the beginning");
        printf("\n 8: Delete a node from the end");
        printf("\n 9: Delete a given node");
        printf("\n 10: Delete a node after a given node");
        printf("\n 11: Delete the entire list");
        printf("\n 12: Sort the list");
        printf("\n 13: EXIT");
        printf("\n\n Enter your option : ");
        scanf("%d", &option);
        switch(option)
        {
            case 1:
                start = create_ll(start);
                printf("\n LINKED LIST CREATED");
                break;
            case 2:
                start = display(start);
                break;
            case 3:
                start = insert_beg(start);
                break;
            case 4:
                start = insert_end(start);
                break;
            case 5:
                start = insert_before(start);
                break;
            case 6:
                start = insert_after(start);
                break;
            case 7:
                start = delete_beg(start);
                break;
            case 8:
                start = delete_end(start);
                break;
            case 9:
                start = delete_node(start);
                break;
            case 10:
                start = delete_after(start);
                break;
            case 11:
                start = delete_list(start);
                printf("\n LINKED LIST DELETED");
                break;
            case 12:
                start = sort_list(start);
                break;
        }
    }while(option !=13);
    getch();
}

struct node *create_ll(struct node *start)
{
    struct node *new_node, *ptr;
    int num;
    printf("\n Enter -1 to end");
    printf("\n Enter the data : ");
    scanf("%d", &num);
    while(num!=-1)
    {
        new_node = (struct node*)malloc(sizeof(struct node));
        new_node -> data=num;
        if(start==NULL)
        {
            new_node -> next = NULL;
            start = new_node;
        }
        else
        {
            ptr=start;
            while(ptr->next!=NULL)
            ptr=ptr->next;
            ptr->next = new_node;
            new_node->next=NULL;
        }
        printf("\n Enter the data : ");
        scanf("%d", &num);
    }
    return start;
}
struct node *display(struct node *start)
{
    struct node *ptr;
    ptr = start;
    while(ptr != NULL)
    {
        printf("\t %d", ptr -> data);
        ptr = ptr -> next;
    }
    return start;
}
struct node *insert_beg(struct node *start)
{
    struct node *new_node;
    int num;
    printf("\n Enter the data : ");
    scanf("%d", &num);
    new_node = (struct node *)malloc(sizeof(struct node));
    new_node -> data = num;
    new_node -> next = start;
    start = new_node;
    return start;
}
struct node *insert_end(struct node *start)
{
    struct node *ptr, *new_node;
    int num;
    printf("\n Enter the data : ");
    scanf("%d", &num);
    new_node = (struct node *)malloc(sizeof(struct node));
    new_node -> data = num;
    new_node -> next = NULL;
    ptr = start;
    while(ptr -> next != NULL)
        ptr = ptr -> next;
    ptr -> next = new_node;
    return start;
}
struct node *insert_before(struct node *start)
{
    struct node *new_node, *ptr, *preptr;
    int num, val;
    printf("\n Enter the data : ");
    scanf("%d", &num);
    printf("\n Enter the value before which the data has to be inserted : ");
    scanf("%d", &val);
    new_node = (struct node *)malloc(sizeof(struct node));
    new_node -> data = num;
    ptr = start;
    while(ptr -> data != val)
    {
        preptr = ptr;
        ptr = ptr -> next;
    }
    preptr -> next = new_node;
    new_node -> next = ptr;
    return start;
}
struct node *insert_after(struct node *start)
{
    struct node *new_node, *ptr, *preptr;
    int num, val;
    printf("\n Enter the data : ");
    scanf("%d", &num);
    printf("\n Enter the value after which the data has to be inserted : ");
    scanf("%d", &val);
    new_node = (struct node *)malloc(sizeof(struct node));
    new_node -> data = num;
    ptr = start;
    preptr = ptr;
    while(preptr -> data != val)
    {
        preptr = ptr;
        ptr = ptr -> next;
    }
    preptr -> next=new_node;
    new_node -> next = ptr;
    return start;
}
struct node *delete_beg(struct node *start)
{
    struct node *ptr;
    ptr = start;
    start = start -> next;
    free(ptr);
    return start;
}
struct node *delete_end(struct node *start)
{
    struct node *ptr, *preptr;
    ptr = start;
    while(ptr -> next != NULL)
    {
        preptr = ptr;
        ptr = ptr -> next;
    }
    preptr -> next = NULL;
    free(ptr);
    return start;
}
struct node *delete_node(struct node *start)
{
    struct node *ptr, *preptr;
    int val;
    printf("\n Enter the value of the node which has to be deleted : ");
    scanf("%d", &val);
    ptr = start;
    if(ptr -> data == val)
    {
        start = delete_beg(start);
        return start;
    }
    else
    {
        while(ptr -> data != val)
        {
            preptr = ptr;
            ptr = ptr -> next;
        }
        preptr -> next = ptr -> next;
        free(ptr);
    }
    return start;

}
struct node *delete_after(struct node *start)
{
    struct node *ptr, *preptr;
    int val;
    printf("\n Enter the value after which the node has to deleted : ");
    scanf("%d", &val);
    ptr = start;
    preptr = ptr;
    while(preptr -> data != val)
    {
        preptr = ptr;
        ptr = ptr -> next;
    }
    preptr -> next=ptr -> next;
    free(ptr);
    return start;
}
struct node *delete_list(struct node *start)
{
    struct node *ptr;
    ptr=start;
    while(ptr!=NULL)
    {
        start=delete_beg(ptr);
        ptr=start;
    }
    free(start);
    return start;
}
struct node *sort_list(struct node *start)
{
    struct node *ptr1, *ptr2;
    int temp;
    ptr1 = start;
    while(ptr1 -> next != NULL)
    {
        ptr2 = ptr1 -> next;
        while(ptr2 != NULL)
        {
            if(ptr1 -> data > ptr2 -> data)
            {
                temp = ptr1 -> data;
                ptr1 -> data = ptr2 -> data;
                ptr2 -> data = temp;
            }
            ptr2 = ptr2 -> next;
        }
        ptr1 = ptr1 -> next;
    }
    return start; // Had to be added
}