在链表中添加列表项或节点

I try the following c++ code to sort linked list Items while inserting value from the keyboard. Here I want to insert values at the beginning, somewhere in the middle and at the end in one Insertion function using while loop. my focus is only on how to insert and delete by finding the exact position using logical operations. Could you please help me in coding a linked list that can sort while inserting an item in c++

#include <iostream>
using namespace std;

struct listItem
    {
    //creating a node
    int data;
    struct listItem *next;
    };
//function declaration
bool Initialize(listItem *head);
char menu();
void insertFirst(listItem *&head, listItem *&temp, int item);
void Insert(listItem *&head, listItem *&temp, int item);
void search(listItem *&head, listItem *&temp);
void deleteItem(listItem *&head, listItem *&temp);
void traverse(listItem *curr);

//function definition
bool Initialize(listItem *head)
    {
    //Initialize head and temp value to null
    listItem *head = NULL;
    listItem *temp = NULL;
    }

char menu()
    {
    //menus 
    char choice;
    cout<<"~~~~~~~~~~~~~~~~~~~~~~~~
";
    cout<<"        Menu"<<endl;
    cout<<"       ........
";
    cout<<"1. Add an Item
";
    cout<<"2. Remove an Item
";
    cout<<"3. Search an Item
";
    cout<<"4. Traverse an Item
";
    cout<<"5. Exit
";
    cout<<"~~~~~~~~~~~~~~~~~~~~~~~~
";

    cin>>choice;
    return choice;
    }
//function to insert items 
void Insert(listItem *&head, listItem *&temp, int item)
    {
    // check if the linked list is null
    listItem *curr = new listItem;
    if(head == NULL)
        {
        curr->data = item;
        curr->next =NULL;
        temp = curr;
        head = curr;
        }
        //check if linked list is not empty and chose the right location
        else if(head->data > item)
            {
            curr->data = item;
            curr->next = temp->next;
            temp = curr;
            }
        //check if linked list is not empty and chose the right location
        else if(head->data < item && curr->next != NULL)
            {
            while (curr->data < item)
            curr = curr->next;
            temp->next = curr;
            curr->data = item;
            curr->next = temp;
            temp = curr;
            }
        //check if linked list is not empty and chose the right location
        else if(head->data < item)
            {
            while(head->data < item && curr->next == NULL)
            curr = curr->next;
            curr->data = item;
            curr->next = NULL;
            temp = curr;
            }
        else
            cout<<item<<" is already there!!!
";
    }

void search(listItem *&head, listItem *&temp)
    {
    cout<<"NO code for searching item"<<endl;
    }
void deleteItem(listItem *&head, listItem *&temp)
    {
    if(Initialize(head))
        cout<<"The list is already Empty
";
    else if(head == temp)
        {
        delete head;
        head = NULL;
        temp = NULL;
        }
    else
        {
        listItem *curr = new listItem;
        head = head->next;
        delete curr;
        }
    }
void traverse(listItem *curr)
    {
    if(Initialize(curr))
        cout<<"The list is already Empty
";
    else
        {
        cout<<"The list contains:
";
        while(curr != NULL)
            {
            cout<<curr->data<<endl;
            curr = curr->next;
            }
        }
    }

int main()
    {

    bool Initialize(head)

    char choice;
    int item;
    do
        {
        choice = menu();
        switch(choice)
            {
            case '1': cout<<"Please enter a number :";
                    cin>>item;
                    Insert(head, temp, item);
                    break;
            case '2': //cout<<"Enter a number to delete :";
                    //cin>>item;
                    deleteItem(head, temp);
                    break;
            case '3': search(head, temp);
                    break; 
            case '4': traverse(head);
                    break;
            default: cout<<"System exit
";
            }
        }
        while(choice != '5');
        return 0;
    }

推荐答案

插入节点.首先...代码！

#include <iostream>

struct listItem
    {
    //creating a node
    int data;
    struct listItem *next;
    };

//function to insert items
void Insert(listItem *&head, int item)
    {
    listItem **curr = &head; // start at head
    while (*curr != NULL // while there is a node
            && (*curr)->data <= item ) //  and the node goes before the new node
        {
        curr = &(*curr)->next; // get next node
        }
    *curr = new listItem{item, *curr}; // insert the new node
    }

int main()
    {

    listItem * head = NULL; // empty linked list head

    Insert(head, 1); // test insert to empty list
    Insert(head, 0); // insert at head
    Insert(head, 3); // insert at end
    Insert(head, 2); // insert in the middle
    }

listItem **curr;

while (*curr != NULL // while there is a node
        && (*curr)->data <= item ) //  and the node goes before the new node
    {
    curr = &(*curr)->next; // get next node
    }

*curr = new listItem{item, *curr};