Thread: Pointers Linked List

This code is from a example in Jumping Into C++ and I understand the example. But it is a practice problem that is to write a program to remove an element from a linked list; the remove function should take just the element to be removed.

Code:

#include <iostream>


using namespace std;


struct EnemySpaceShip
{
    int x_coordinate;
    int y_coordinate;
    int weapon_power;
    EnemySpaceShip *p_next_enemy;
};


EnemySpaceShip *getNewEnemy()
{
    EnemySpaceShip *p_ship = new EnemySpaceShip;
    p_ship->x_coordinate = 0;
    p_ship->y_coordinate = 0;
    p_ship->weapon_power = 20;
    p_ship->p_next_enemy = NULL;
    return p_ship;
}


void updateShip(EnemySpaceShip *p_ship)
{
    p_ship->x_coordinate += 10;
    p_ship->y_coordinate += 10;
    p_ship->weapon_power += 20;


    cout << "X: " << p_ship->x_coordinate << endl;
    cout << "Y: " << p_ship->y_coordinate << endl;
    cout << "Weapon Power: " << p_ship->weapon_power << endl;
}


int main()
{
    EnemySpaceShip *getShip = getNewEnemy();
    updateShip(getShip);
    return 0;
}

If I got this right I will create a pointer that points to the first SHIP (getNewEnemy) and the other one will not be printed out.

I have seen the code example and I know that it isn't creating a linked list. But I have no idea of how to write a program that removes a element from a linked list. Is it any website or something exaplaining linked list. Or hints that somebody can give to help me? It is one of the practice problems in Jumping Into C++ and I want to do all of them so you really can understand how pointers work

The way to remove a singly linked list node is to point the previous node's next link to the node after the one you delete. If the remove function can only take a pointer to the node to delete, the linked list should be a doubly linked list. As a singly linked list, remove(node *removeMe) can't work: there is no way to access the previous node to the deleted node without a pointer to it.

Making the linked list doubly linked also makes the removal more complicated. You have to set the previous nodes next link to point to the next node, and the next node's prev link to point to the previous node. In exchange though, remove(node *removeMe) does work.

Once you reset the previous and next links, you can safely release the memory of the old node.

Elysia, may I direct you to reread the OP's post.

Originally Posted by DecoratorFawn82

the remove function should take just the element to be removed.

An extra parameter, a pointer to the list, is not allowed, AFAICT.