List_Delete

/*Sorting from little to large use List*/

#include <stdio.h>         /* printf, scanf, NULL */
#include <stdlib.h>     /* malloc, free */

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

typedef struct node Node;

Node *Head = NULL;
Node *current;

void Insert(int k)
{
    Node *new_node;

    new_node = (Node *)malloc(sizeof(Node));//It is important but i can't understand now

    new_node->key = k;

    /* new node is inserted at the begining of the list*/

    if ( Head == NULL || Head->key > k )
    {
        new_node->next = Head;
        Head = new_node;
    }

    /* new node is inserted somewhere inside the list */
    else
    {
        current = Head;

        /* Check what is the value in the next node , after the current node */
        /* if it is larger, or if the next node not exist */
        /* then we shuold insert the node to next current */
        /* else, update current to point to next node */

        while()
        {
            if( current->next == NULL || current->next->key > k )
            {
                new_node->next = current->next;
                current->next = new_node;
                break;
            }
            else
                current = current->next;
        }
    }
}

Node *Delete(int k)
{
    Node *answer;
    Node *current = Head;

    /* Handle the special case that the first node is to be deleted */
    if ( Head != NULL && Head->key == k )
    {
        Head = Head->next;
        return current;
    }

    else if ( Head != NULL && Head->key > k )
    {
        return NULL;
    }

    while( current != NULL )
    {
        /* check the next node is to be deleted */
        if ( current->next != NULL && current->next->key == k )
        {
            answer = current->next;
            current->next = current->next->next;
            return answer;
        }

        else if ( current->next != NULL && current->next->key > k )
            return NULL;

        /* else, updated current */
        current = current->next;
    }
    return NULL;

    /* if current is NULL, then k is not in the list, to return NULL */ 

} 

void Print()
{
        if( Head == NULL )
        printf("The list is empty!\n");
    else
    {
        current = Head;

        while( current != NULL )
        {
            printf("%d ", current->key);
            current = current->next;
        }

        printf("\n");
    }
}

int main()
{
    Node *x;

    Insert();
    Insert();
    Insert();

     printf("15, 12, 5 are inserted");

     Print();

     x = Delete();
     if (x != NULL )
     {
         printf("5 is deleted: ");
        free(x);
        Print();
    }

    x = Delete();
    if ( x != NULL )
    {
        printf("12 is deleted: ");
        free(x);
        Print();
    }

    Insert();
    Insert();
    Insert();

    printf("6, 8, 7 is inserted: ");
    Print();

    x = Delete();
    if ( x != NULL )
    {
        printf("8 is deleted: ");
        free(x);
        Print();
    }     

    return ;
}