Vector Class (ex. Velocity Vector not Vector from STL) Problem

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http://www.daniweb.com – I have been trying to make a vector class to handle particles in a particle system I am making. The problem I have is when I try to change the dir it does not do what it is supposed to. If I keep pressing up it will just bounce back from between two directions same with down. But if I go up down repeatedly it changes a little bit but not much. I cannot figure out why this is happening. This is my class struct sPosition{float x,y;}; class cVector{     float Mag;     sPosition Pos;     sPosition Dir;     public:     cVector(float PosX = 0.0f,float PosY = 0.0f, float Magn = 0.0f, float Degrees = 0.0f){         Pos.x = PosX;         Pos.y = PosY;         SetDirD(Degrees);         Mag = Magn;     }     float GetPosX(){return Pos.x;}     float GetPosY(){return Pos.y;}     float GetDirX(){return Dir.x;}     float GetDirY(){return Dir.y;}     float GetDirR(){return float (atan2(Dir.x,Dir.y * -1.0f));}     float GetMag(){return Mag;}     void SetPos(float PosX,float PosY){Pos.x = PosX; Pos.y = PosY;}     void SetDir(float DirX,float DirY){Dir.x = DirX; Dir.y = DirY;}     void SetDirR(float Rads){         Dir.x = float (cos(Rads));         Dir.y = float (sin(Rads) * -1.0);     }     void SetDirD(float Degs){         Dir.x = float (cos(DegToRad<float>(Degs)));         Dir.y = float (sin(DegToRad<float>(Degs)) * -1.0);     }     void SetMag(float Magn){Mag = Magn;} }; this is my main.cpp just in case it is useful. I am using sfml graphics library btw. #include <SFML/Graphics.hpp> #include "Vectors.h" sf::RenderWindow App(sf::VideoMode(800, 600, 32), "SFML Graphics"); int main(){     cVector VectA(200.0f,300.0f,100.0f,45.0f);     // Create the main rendering window     // Start game loop     while (App.IsOpened())     {         sf::Event Event;         while (App.GetEvent(Event)){             // Close window : exit             if (Event.Type == sf::Event::Closed)                 App.Close();             if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Up))                 VectA.SetDirR(VectA.GetDirR() + 0.1f);             if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Down))                 VectA.SetDirR(VectA.GetDirR() - 0.1f);         }         // Clear the screen (fill it with black color)         App.Clear();         App.Draw(sf::Shape::Line(VectA.GetPosX(),VectA.GetPosY(),                                 VectA.GetPosX() + (VectA.GetDirX() * VectA.GetMag()),                                 VectA.GetPosY() + (VectA.GetDirY() * VectA.GetMag()),                                 2.0f,sf::Color::Red));         App.Display();     }     return EXIT_SUCCESS; } (General)