The graph plotter application

The graph plotter application is a simple WPF application with a canvas and a textbox in the frame. The following image gives a snapshot of the screen after the screen has rendered the result of an expression:

The WPF canvas gets a notification whenever there is a change in the expression textbox. If the expression in the textbox is valid, the graph will be plotted as shown in the preceding image. We will deal with the nuances of implementing an expression evaluation engine in the following sections. The following code snippet shows how the change in text gets handled:

    public override void  
    Observer_ExpressionChangedEvent( string expression) 
    { 
      MainWindow mw = this._ctrl as MainWindow; 
      mw.Expr = expression; 
      ExpressionBuilder builder = new  
      ExpressionBuilder(expression); 
      Exp expr_tree = builder.GetExpression(); 
 
      if ( expr_tree != null ) 
      mw.Render(...