title: Can anyone help me understand this error? "definition of implicitly-declared ‘classA::classA()’"
body: <p>Heres the code:</p>
  
  <pre><code>#include &lt;cstdlib&gt;
  #include &lt;iostream&gt;
  using namespace std;
  
  class classA
  {                   
        protected:
                  void setX(int a);
  
        private:
                int p;
  };
  
  classA:: classA()
  {                      //error here.
   p = 0;
  }
  
  void classA:: setX(int a)
  {
   p = a;    
  }
  
  int main()
  {   
      system("PAUSE");
      return EXIT_SUCCESS;
  }
  </code></pre>