Can't find the access violation problem (NULL pointer?)

#ifdef WIN32
#pragma comment(lib, "SDL.lib")
#pragma comment(lib, "SDLmain.lib")
#endif

//#include <iostream>
//#include "Blok.h"
//#include "ColorMath.h"
//#include "Swatch.h"
#include "Engine.h"

//using namespace std;

int main(int argc, char *argv[])
{
	/*Blok Block1(1,1,BLACK,false);
	Blok Block2(2,2,RED,false);
	cout << Block1.get_color() << endl;
	cout << Block2.get_color() << endl;
	mix(Block1,Block2);
	cout << Block1.get_color() << endl;
	cout << Block2.get_color() << endl;
	cin.get();*/

	Engine theEngine;

	theEngine.SetTitle("SDL_Stuff");
	theEngine.Init();

	return 0;
}

#include "Engine.h"

Engine::Engine()
{
	winWidth = 800;
	winHeight = 600;
	winTitle = 0;
	winScreen = 0;
}

Engine::~Engine()
{
	SDL_Quit();
}

void Engine::Input()
{
}

void Engine::Render()
{
}

void Engine::Logic()
{
}

void Engine::SetSize(const int& width, const int& height)
{
	winWidth = width;
	winHeight = height;
	winScreen = SDL_SetVideoMode( width, height, 0, SDL_ANYFORMAT);
}

SDL_Surface* Engine::GetScreen()
{
	return winScreen;
}

void Engine::Init()
{

	if( SDL_Init(SDL_INIT_VIDEO) < 0)
	{
		fprintf(stderr,"SDL failed to initalize.");
		SDL_Quit();
	}

	SetSize( winWidth, winHeight);

	if( winScreen == NULL)
	{
		fprintf(stderr,"SDL failed to display screen.");
		SDL_Quit();
	}
}

void Engine::Loop()
{
}

void Engine::SetTitle(const char* title)
{
	winTitle = title;
	SDL_WM_SetCaption( title, 0);
}