Richtextbox as a C# editor.

string pattern = "";
     string[] keywords =
     {
         "bool","void","return","function","string","object",
     };



     foreach (var a in keywords)
     {
         pattern += a + "|";
     }



     Regex R = new Regex(pattern);
     int index = rtbExpression.SelectionStart;



     foreach (Match m in R.Matches(rtbExpression.Text))
     {
         rtbExpression.Select(m.Index, m.Value.Length);
         rtbExpression.SelectionColor = Color.Blue;
         rtbExpression.SelectionStart = index;
     }



     rtbExpression.SelectionColor = Color.Black;



     rtbExpression.ShortcutsEnabled = true;