title: C++ error: definition of implicitly-declared
body: <p>I'm writing this linked list program with C++</p>
  
  <p>When I test the program, I got the error</p>
  
  <blockquote>
    <p>linkedlist.cpp:5:24: error: definition of implicitly-declared 'constexpr LinkedList::LinkedList()'
    LinkedList::LinkedList(){</p>
  </blockquote>
  
  <p>Here's the code</p>
  
  <p>linkedlist.h file:</p>
  
  <pre><code>#include "node.h"
  using namespace std;
  
  class LinkedList {
    Node * head = nullptr;
    int length = 0;
  public:
    void add( int );
    bool remove( int );
    int find( int );
    int count( int );
    int at( int );
    int len();
  };
  </code></pre>
  
  <p>linkedlist.cpp file:</p>
  
  <pre><code>#include "linkedlist.h"
  #include &lt;iostream&gt;
  using namespace std;
  
  LinkedList::LinkedList(){
    length = 0;
    head = NULL;
  }
  /*and all the methods below*/
  </code></pre>
  
  <p>please help.</p>