title: C++ variable array as class member
body: <p>I have a small C++ program defined below:</p>
  
  <pre><code>class Test
  {
     public:
     int a;
     int b[a];
  };
  </code></pre>
  
  <p>When compiling, it produces an error:</p>
  
  <pre><code>testClass.C:7:5: error: invalid use of non-static data member ‘Test::a’
  testClass.C:8:7: error: from this location
  testClass.C:8:8: error: array bound is not an integer constant before ‘]’ token
  </code></pre>
  
  <p>How do I learn about what the error message means, and how do I fix it?</p>