title: Undefined reference to '(all my functions)'
body: <p>I'm getting all these errors:</p>
  
  <blockquote>
    <p>undefined reference to 'getLength()'<br>
       undefined reference to 'getWidth()'<br>
       undefined reference to 'getArea(double, double)'<br>
       undefined reference to 'displayData(double, double, double)'  </p>
  </blockquote>
  
  <p>Here's my code:</p>
  
  <pre><code>#include &lt;iostream&gt;
  
  using namespace std;
  
  double getLength();
  double getWidth();
  double getArea(double,double);
  void displayData(double,double,double);
  
  int main()
  {
      double length;
      double width;
      double area;
  
      length = getLength();
      width = getWidth();
      area = getArea(length,width);
      displayData(length,width,area);
  
      return 0;
  }
  
  //getLength function
  double getLength();
  {
  
      double length;
      cout &lt;&lt; "Length: ";
      cin &gt;&gt; length;
  
      return length;
  
  }
  
  //getWidth function
  double getWidth();
  {
      double width;
      cout &lt;&lt; "Width: ";
      cin &gt;&gt; width;
  
      return width;
  }
  
  //GetArea function
  double getArea(double lenght, double width);
  {
      return length*width;
  }
  
  //displayData function
  void displayData(double length, double width, double area);
  {
      cout &lt;&lt; "\nRectangle Data\n"
          &lt;&lt; "---------------\n"
          &lt;&lt; "Length: " &lt;&lt; length &lt;&lt; endl
          &lt;&lt; "Width: " &lt;&lt; width &lt;&lt; endl
          &lt;&lt; "Area: " &lt;&lt; area &lt;&lt; endl;
  
  }
  </code></pre>