title: Redefinition of class error
body: <p>I am designing a program that takes three given points and calculates the fourth to create a parallelogram. What I have so far is:</p>
  
  <pre><code>struct Parallelogram : public Polygon {
      Parallelogram(Point tl, Point tr, Point bl){
          Point br;
          int num = tr.y-tl.y;
          int denom = tr.x-tl.x;
          br.x=denom+bl.x;
          br.y=num+bl.y;
      }
  };
  
  Parallelogram::Parallelogram(Point tl, Point tr, Point bl)
  {
      add(tl);
      add(tr);
      add(bl);
      add(br);
  };
  </code></pre>
  
  <p>I get the following error when compiling:</p>
  
  <pre><code>hw6pr2.cpp:15:1: error: redefinition of âParallelogram::Parallelogram(Point, Point, Point)â
  hw6pr2.cpp:6:2: error: âParallelogram::Parallelogram(Point, Point, Point)â previously defined here
  </code></pre>
  
  <p>My question is: If the way I am deriving from the polygon class correct? If so why am I getting this error?</p>