Thread: Chapter 15 - Practice Problem1

I'm a beginner at C++ and I'm currently reading the "Jumping into C++" book. I'm currently at chapter 15 doing practice problem 1.

Practice problem 1 basically says to write a program to remove an element from a linked list; the remove function should take just the element to be removed.

Here's my code so far:

Code:

#include <iostream>

using namespace std;


struct Spaceship 
{
    int x;
    int y;
    int power;
    Spaceship* pNextSpaceShip;
};


Spaceship* addNewShipToList(Spaceship* pList);


void removeShipFromList(Spaceship* pLast, Spaceship* pList);




Spaceship* pShipList;


int main()
{
    pShipList = NULL;
    
    
    int counter = 0;
    // add 9 elements to the linked list
    for(int i = 0; i < 9; ++i)
    {
        pShipList = addNewShipToList(pShipList);
    }


    // set the current to the first element in the list
    Spaceship* pCurrent = pShipList;
    // traverse through our list to verify how many elements are in the list
    while(pCurrent != NULL)
    {
        pCurrent = pCurrent->pNextSpaceShip;
        counter++;
    }


    cout << "The linked list contains " << counter << " ships" << endl;
    
    // reset counter to 0
    counter = 0;


    // create a new pointer that points to the first element
    Spaceship* pLast = pShipList;
    // remove the first element from the list
    removeShipFromList(pLast, pShipList);
    
    // set the current to the 'new' first element of the list
    pCurrent = pShipList;
    
    // traverse through the list again to verify that one element from the list has been deleted
    while(pCurrent != NULL)
    {
        pCurrent = pCurrent->pNextSpaceShip;
        counter++;
    }
    cout << "The linked list contains " << counter << " ships" << endl;
    


    cin.ignore();
    cin.get();


    return 0;
}






Spaceship* addNewShipToList(Spaceship* pList)
{
    // to use this function, use
    //list = addNewShipToList(list);
    //////////////////////////////////
    Spaceship* pShip = new Spaceship;
    pShip->x = 0;
    pShip->y = 0;
    pShip->power = 20;
    pShip->pNextSpaceShip = pList;


    return pShip;
}


void removeShipFromList(Spaceship* pLast, Spaceship* pList)
{
    pList = pList->pNextSpaceShip;
    delete pLast;


}

I'm running to a run-time error when the program reaches the inside of the 2nd while-loop, specifically at line 57 which is

Code:

pCurrent = pCurrent->pNextSpaceShip;

I think the way I wrote my removeShipFromList function is wrong. Can anyone help me figure this out?

Thanks

Removing a node from a linked list using only the node to delete as a starting point requires that the list be doubly linked. Then you can do these four lines:

Code:

if (old->next != NULL )
  old->next->prev = old->prev;
if (old->prev != NULL )
  old->prev->next = old->next;

Now as far as the list is concerned, old isn't in there. You can free old's memory.