C ++ Can't increment variable

I am working on an animation class for a small game engine and for some reason the frame counter doesn't want to increase, it stays at 0 or 1.

This is the Animation :: Step code (where increment is assumed here):

void Animation::Step()
{
    ...

    time += (float)glfwGetTime();
    if (time >= Speed)
    {
        time = 0;
        if (f++ >= count - 1)
        {
            ...
        }
    }

    // Here I do some math to get a clip rectangle...

    ...
}

      

        
        
        
      

    

Now this is the part where the :: Step animation is called:

inline void DrawAnimation(Animation ani, Vec2 pos, BlendMode mode, DrawTextureAttributes attr)
{
    ani.Step();

    ...
    // draw texture
}

      

        
        
        
      

    

And in the mainloop game:

void on_render(Renderer r)
{
    DrawTextureAttributes attr;
    attr.Scale = Vec2(1.5);

    r.DrawAnimation(ani, Vec2(320, 240), BlendMode::Normal, attr);
}

      

        
        
        
      

    

EDIT: Class definition:

class Animation
{
public:
    Animation() {}
    Animation(Texture2D tex, int rows, int cols, int *frames, float speed, bool loop=false);
    Animation(Texture2D tex, int rows, int cols, float speed, bool loop=false);

    Texture2D Texture;
    std::vector<int> Frames;
    float Speed;
    bool Loop;

    float getCellWidth();
    float getCellHeight();

    void Step();

    UVQuad RETUV;

private:
    int f, r, c; // here F 
    float w, h;
    float time;
};

      

        
        
        
      

    

Ok, thanks in advance! (and sorry for my curious bad english)