Adding value to end of linked list and removing from the front c++

Question

I'm attempting to add items to the end of the list and remove them from the beginning of the list. The program compiles but crushes when I try to add items. I'm new to this concept an it's taking some time to settle in completely. Any help is appreciated.. Thanks!

  #include<iostream>
using namespace std;



struct myNode
{
    int val;
    struct myNode *next;
};


class Cll
{

public:
    myNode* head = new myNode;
    myNode* tail = new myNode;

    Cll()
    {
        head = NULL;
        tail = NULL;
    }
    myNode* createAnode(int value)
    {
        myNode* temp;
        temp = new myNode;

        temp->val = value;
        temp->next = NULL;
        return temp;
    }
    void addingValues()
    {
        int numb;
        cout<<"Enter the number to be added: ";
        cin>>numb;
        myNode *temp, *p;
        temp = createAnode(numb);

        p = head;
        p = p-> next;
       temp -> next = NULL ;
        p -> next = temp;

    }
        void deletingValues()
    {
        myNode *s;
        s = head;
        head = s->next;
    }

     void showValues()
    {
        struct myNode *temp2;

        temp2 = head;
        while (temp2)
        {
            cout<<temp2->val<<"->";
            temp2 = temp2->next;
        }
        cout<<"NULL"<<endl;
    }

};



int main()
{

    int pick ;
    Cll cll;
    int again;




    do
    {

        cout<<"1.add"<<endl;
        cout<<"2.delete"<<endl;
        cout<<"3.show"<<endl;
        cout<<"Enter choice : ";
        cin>>pick;
        switch(pick)
        {
            case 1:
                cll.addingValues();
                cout<<endl;
                break;

            case 2:
                cll.deletingValues();
                break;
            case 3:
                cll.showValues();
                cout<<endl;
                break;

        }
        cout << "Enter 1 to see again, enter 2 to quit"<< endl;
        cin >> again;

    } while (again == 1);




}

Answer 1

You are programming in c++, so I recommend to use std::list.

But if you like to do it yourself, and you like to ad a node at front of your single liked list, you first have to check if it is the first node or not. If it is the first node your new node ist head and tail. If not the new node is the the head and its successor is the old head of the list. Adapt your code like this:

void addingValues()
{
    int numb;
    cout << "Enter the number to be added: ";
    cin >> numb;
    myNode  *newNode = createAnode(numb);

    if ( head == NULL ) // if list is empty the new node is the head and the tail
    {
        head = tail = newNode;
        return;
    }

    tail->next = newNode; // successor of last node is new node and new node is tail
    tail = newNode;
}

To delete a node from front of the list you have to check if the list is not empty and if it was the last node in the list:

void deletingValues()
{
    if ( head == NULL )
        return;

    myNode *temp = head->next;
    delete head;
    head = temp;
    if ( head == NULL )
        tail == NULL;
}