title: What's a sync and async method?
body: <p>What's a sync method and what is an async method ? What's the difference between sync and async methods ? When do I have to use sync or async method ?
  I'm asking those questions because I don't understand :</p>
  
  <pre><code>public async void ReadData(filepath)
  {
      CreateDoc("hello");    //&lt;------ Why I can't do that ?
  }
  
  public void CreateDoc(string astring)
  {
      Debug.WriteLine(astring);
  }
  </code></pre>
  
  <p>And why I can't do that ? :</p>
  
  <pre><code>public async void ReadData(filepath)
  {
       var BarreDroite = new string[] { "|" };
       foreach (string tableArret in items.Split(BarreDroite, StringSplitOptions.RemoveEmptyEntries))
       {
           listeArret.Add(tableArret); //&lt;---- Here appear the problem.
       }
  {
  </code></pre>
  
  <p>I ask this question because I don't really find clear explanations on the web.</p>