why doesn't this work

///////////////// TerrainWindow.hpp
#include "BasicInclude.h"
class TerrainWindow
{
    // terrain window
public:
    void CreateTerrainWindow(int width, int height, int bits, std::string title);
//  sf::RenderWindow GetTerrainWindow();
    void TerrainWindowLoop();
//  bool GetState();
//  void SetState(bool running);
    void CreateSinWave();
    void AddDrawable(sf::Sprite newDrawable);
    void Draw();
private:
    sf::RenderWindow Wnd;
//  bool isRunning;
//  sf::Sprite sinWave;
    std::vector<sf::Sprite> sprites;
};

void TerrainWindow::CreateTerrainWindow(int width, int height, int bits, std::string title)
{
    Wnd.create(sf::VideoMode(width, height, bits), title);
}

void TerrainWindow::AddDrawable(sf::Sprite newDrawable)
{
    sprites.push_back(newDrawable);
}
void TerrainWindow::Draw()
{
    for(int i = 0; i <= sprites.size(); i++)
    {
        Wnd.draw(sprites.at(i));
        std::cout << i << "\n";
        std::cout << sprites.size();
    }
}
void TerrainWindow::TerrainWindowLoop()
{
    while(Wnd.isOpen())
    {
        sf::Event events;
        while (Wnd.pollEvent(events))
        {

            if (events.type == sf::Event::Closed)
                Wnd.close();
        }
        Wnd.clear();
        TerrainWindow::Draw();
        Wnd.display();
    }
}

///////////////// Entity.hpp
#include "BasicInclude.h"

class Entity : public sf::Sprite
{
public:
    void textureInit(std::string file);
private:
    sf::Texture texture;
};

void Entity::textureInit(std::string file)
{
    if(!texture.loadFromFile(file))
    {
        std::cout << "Error opening " << file << "\n";
    }
    else
    {
        this->setTexture(texture);
    }
}

///////////////// main.cpp
#include "TerrainWindow.hpp"
#include "Entity.hpp"
int main()
{
    TerrainWindow wnd;
    wnd.CreateTerrainWindow(800, 600, 32, "Test of SFML Engine");

    Entity ent, ent2;
    ent.textureInit("dot.png");
    ent.setPosition(10.0f, 10.0f);

    ent2.textureInit("dot.png");
    ent2.setPosition(100.0f, 100.0f);

    wnd.AddDrawable(ent);
    wnd.AddDrawable(ent2);

    wnd.TerrainWindowLoop();
}
//