Linked List Problem

[Paul Christopher]

I'm working on a linked list version of my asteroids program. I run into an error when I change it from a vector to a linked list. I'm not sure how to go about fixing it. Any help would be appreciated.

// Dark GDK - The Game Creators - www.thegamecreators.com

// the wizard has created a very simple project that uses Dark GDK
// it contains the basic code for a GDK application

// whenever using Dark GDK you must ensure you include the header file
#include "DarkGDK.h"
#include <ctime>
#include <list>

class Asteroids {
public:

	Asteroids() {
		
		//Set Asteroid ID
		ast_id = numObjects;
		astDestroyed = false;


		//Variables
		astx = rand() %700;
		asty = rand() %500;
		astx_cnt = 2;
		asty_cnt = 2;
		asrotate = 0;

		numObjects++;
	}

	~Asteroids() {
		

		numObjects--;
	}

	static int numObjects;

	void Location () {

		//Asteroid Variables
		asmove = 0;
		
		//Check Value of Asteroid
		if (astDestroyed)
			return;

		//Asteroid Movement Variables
		dbSprite(ast_id,astx,asty,2);
		astx = astx + astx_cnt;
		asty = asty + asty_cnt;
		//astx_inc = astx+1;
		//asty_inc = asty+1;

	
		//Rotate Asteroid 1
		asrotate = asrotate +5;
		dbRotateSprite(ast_id,asrotate);
		
		//Place Asteroid Sprite
		if (dbSpriteExist(ast_id))
		{
			
			dbOffsetSprite(ast_id,28,29);

			if (asty >= 520) 
			{
				asty_cnt = (asty_cnt * (-1));
			}

			if (astx >= 700)
			{
				astx_cnt = (astx_cnt * (-1));
			}

			if (asty <=-100)
			{
				asty_cnt = (asty_cnt * (-1));
			}

			if (astx <=-100)
			{
				astx_cnt = (astx_cnt * (-1));
			}
		}

		Collision(ast_id);
	}

	void Collision(int ast_id){

		int astx1;
		int asty1;

		//Circular Collision Variables
		radius = 28 + 22;
		shipx = dbSpriteX(1);
		shipy = dbSpriteY(1);
		distx = shipx - astx;
		disty = shipy - asty;

		//Circular Collision
		if (dbSpriteExist(ast_id))
		{
			astx1 = dbSpriteX(ast_id);
			asty1 = dbSpriteY(ast_id);
		}

		//set collision for ship and asteroids
		if (dbSpriteExist(ast_id))
		{
			if ((radius * radius) > (distx * distx) + (disty * disty))
			{
				dbDeleteSprite(1);
			}
		}
		
		if (dbSpriteExist(3))
		{
			dbMoveSprite(3,10);

			if (dbSpriteHit(ast_id,3))
			{
				dbDeleteSprite(ast_id);
				dbDeleteSprite(3);
				astDestroyed = true;
			} 
		}
	}
		

	private:

	//Asteroid Variables
	int asrotate;
	int asmove;
	int ast_id;
	
	int astx;
	int asty;
	
	//Asteroid Movement Variables
	int astx_inc;
	int asty_inc;
	int astx_cnt;
	int asty_cnt;

	//Circular Collision Variables
	int radius;
	int shipx;
	int shipy;
	int distx;
	int disty;
	bool astDestroyed;



};

int Asteroids::numObjects=5;

// the main entry point for the application is this function
void DarkGDK ( void )
{
	// turn on sync rate and set maximum rate to 60 fps
	dbSyncOn   ( );
	dbSyncRate ( 60 ); 
	dbSetWindowSize(600,400); 
	
	//Random Asteroid Location
	srand ((unsigned int) time(0));

	//Load Images
	dbLoadImage("ship.png",1);
	dbLoadImage("pokeball.png",2);
	dbLoadImage("bullet.png",3);

	//Ship Variables
	int shiprotate = 0;

	//Bullet Variables
	int bulletx;
	int bullety;

	//Place Ship Sprite
	dbSprite(1,300,250,1);
	dbOffsetSprite(1,26,26);
		
	
	std::list<Asteroids*> asteroid;
		for (int i=0; i<10; ++i){
			asteroid.push_back(new Asteroids);
		}
	// our main loop
	while ( LoopGDK ( ) )
	{
		for (unsigned int i=0; i<asteroid.size(); ++i){
			asteroid[i]->Location();
		}

		
		//Bullet
		bulletx = dbSpriteX(1);
		bullety = dbSpriteY(1);

		//Ship Movement (stays in the main loop)
		if (dbUpKey())
		{
			dbMoveSprite(1,5);
		}
		if (dbDownKey())
		{
			dbMoveSprite(1,-5);
		}
		if (dbLeftKey())
		{
			shiprotate = shiprotate -5;
			dbRotateSprite(1,shiprotate);
		}
		if (dbRightKey())
		{
			shiprotate = shiprotate +5;
			dbRotateSprite(1,shiprotate);
		}

		if (dbKeyState(0x39))
		{
			dbSprite(3,bulletx,bullety,3);
			dbRotateSprite(3,shiprotate);
			dbMoveSprite(3,5);
			dbOffsetSprite(3,5,5); 
		}
		
		// update the screen
		dbSync ( );
	}

	// return back to windows
	return;
}

[Gaminic]

for (unsigned int i=0; i<asteroid.size(); ++i){
    asteroid[i]->Location();
}

Linked Lists don't feature random access. That's the only way they can guarantee their efficiency and flexibility.

Since you're looping through the list anyway, you can use an iterator that starts at begin(), stops when it reaches end() and increase the iterator rather than an index.

Can't really find the iterator page itself, but here's a little snippet(*):

for (list<int>::iterator it = fifth.begin(); it != fifth.end(); it++)
    cout << *it << " ";

The iterator is basically a pointer to a "current item". Increasing the iterator jumps to the next item. To use the item, dereference it (or use arrow notation to access members).

* http://www.cplusplus.com/reference/stl/list/list/