title: Where and how to define member variables? In header or implementation file?
body: <p>I have problems understanding the concept of classes and member variables in C++.
  Given the following example:</p>
  <p>File: Mems.h:</p>
  <pre><code>class Mems{
  
  int n;
  Mems();
  };
  </code></pre>
  <p>File Mems.cpp:</p>
  <pre><code>class Mems{
  
  Mems::Mems(){
      //Do something in constructor
  }
  };
  </code></pre>
  <p>I do not know, where I have to put my variables if I want them to stick to the object?</p>
  <p>When I define them in the header-file I can't access them in the cpp File and vice versa.</p>