Im stuck with tutor. #1

[Ilya83]

Im new in SFML and Im new in C++ too And I don't even speak engl. (OMG What am I doing in here  ) Just want to do the video tutor 1 But seems Im stuck. I can't use the "constexpr" So I decided to use just CONST And I got the problem witch i can't solve The problem is "Vector2f velocity". Any help please   

#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>

using namespace std;
using namespace sf;

const unsigned WINDOW_WIDTH = 800;
const unsigned WINDOW_HEIGHT = 600;
const float BALL_RADIUS = 10.f;
const float BALL_VELOCITY = 8.f;

struct Ball
{
    CircleShape shape;

    Vector2f velocity(-BALL_VELOCITY, -BALL_VELOCITY);

    Ball(float mX, float mY)
    {
        shape.setPosition(mX, mY);
        shape.setRadius(BALL_RADIUS);
        shape.setFillColor(Color::Red);
        shape.setOrigin(BALL_RADIUS, BALL_RADIUS);
    }

    void update(){shape.move(velocity);}
};

int main()
{
    Ball ball(WINDOW_WIDTH / 2, WINDOW_HEIGHT / 2);

    RenderWindow window(VideoMode(WINDOW_WIDTH, WINDOW_HEIGHT), "Arkanoid-1");
    window.setFramerateLimit(60);

    while(true)
    {
        Event event;
        window.pollEvent(event);

        window.clear(Color::Black);

        if(Keyboard::isKeyPressed(Keyboard::Escape)) break;

        ball.update();
        window.draw(ball.shape);
        window.display();
    }

    return 0;
}
 

[eXpl0it3r]

Well can you describe what the problem actually is? Like compiler error? Runtime error?

[Ilya83]

My problem is

const float BALL_VELOCITY = 8.F;
Vector2f velocity(-BALL_VELOCITY,-BALL_VELOCITY);
The compil says : expected identifier before '-' token

If I delet '-' Comp. says : BALL_VELOCITY is not a type
(os windows, qt creator(gcc))

[amir ramezani]

because BALL_VELOCITY is a variable not a type
and you must not plase a - character before it

[eXpl0it3r]

That's not the problem here, instead it's because his compiler doesn't support C++11, thus he can't init member variables a declaration.
Instead I suggest to add a simple constructor that inits the variable in the initialization list.

Also I highly recommend to get a C++11 compiler. The video tutorials make heavy use of new features, it will be quite hard to follow them without C++11.

[Ilya83]

added the QMAKE_CXXFLAGS += -std=c++11 in my .pro file And now I'm using C++11 The problem solved Thanks everyone 

[eXpl0it3r]

Ah you didn't have it activated!

Now you might also be able to use constexpr.

[Ilya83]

I'm using it right away!  But didn't find anything about constexpr    Now I'm trying to figure out why he use the brace in setSize func and doesn't use it in setOrigin func 

 shape.setSize({paddleWidth, paddleHeight});

 shape.setOrigin(paddleWidth / 2.f, paddleHeight /2.f);
 

[eXpl0it3r]

That's essentially a question for Laurent, why do so function have an overload for (float, float) while others have just the (sf::Vector2f)? (I bet there have been a few posts about this already...)

Given that I haven't watched the video and thus don't know if he has actually said something about it, I simply assume, that he used the uniform initialization (curly brackets) for the setSize function, because it only accepts an sf::Vector2f, which will get created on the fly with those brackets and you don't have to type the full class name. For the setOrigin function he uses the "native" overload of (float, float), because it's there.
Some might argue about not having to construct a temporary sf::Vector2f object, but that really doesn't matter. Much more interesting would be a discussion about consistency, like when should one use the overloads (if existing) and when should one use the vector directly.

In any case the width and height, could've also been packaged into a sf::Vector2f in the first place, making the code more compact, but maybe introducing more challenge for teaching the code.

[Ilya83]

silly me shape.setSize({paddleWidth, paddleHeight}); has curly brackets cos setSize has only 1 parameter !