Inside the Mathematical Expressions Evaluator

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using SevenZ.Calculator;

namespace Calc
{
   public partial class FormMain : Form
   {
      Calculator clc = new Calculator();
      FormVariables formVars;

      public FormMain()
      {
         InitializeComponent();
      }

      private void btnCount_Click(object sender, EventArgs e)
      {
         try
         {
            txtOut.Text = clc.Evaluate(txtIn.Text).ToString();
            lstLog.Items.Insert(0, txtIn.Text);
            txtIn.Clear();
            txtIn.Select();
         }
         catch (CalculateException ex)
         {
            MessageBox.Show(ex.Message, "Calaculator error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            txtIn.Select();
            txtIn.SelectionStart = ex.TokenPosition;
            txtIn.SelectionLength = 1;
         }
         catch (Exception ex)
         {
            MessageBox.Show(ex.Message + "\r\nPlease check if any of binary functions is missing one of it's input parameters", 
            "Calaculator error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            txtIn.Select();
         }
      }

      private void btnVariables_Click(object sender, EventArgs e)
      {
         if (formVars == null || formVars.IsDisposed)
         {
            formVars = new FormVariables(clc);
            formVars.Location = new Point(this.Left + this.Width + 50, this.Top);

            formVars.Show(this);
         }
         else
            formVars.Visible = !formVars.Visible;
            
      }

      private void FormMain_Shown(object sender, EventArgs e)
      {
         btnVariables_Click(null, null);
         this.Select();
      }

      private void lstHistory_SelectedIndexChanged(object sender, EventArgs e)
      {
         if (lstLog.Items.Count > 0)
            txtIn.Text = lstLog.SelectedItem.ToString();
      }

      private void btnReset_Click(object sender, EventArgs e)
      {
         clc.Reset();
         lstLog.Items.Clear();
      }

      private void txtIn_KeyUp(object sender, KeyEventArgs e)
      {
         switch (e.KeyData)
         {
            case Keys.Up:

               if (lstLog.SelectedIndex > 0)
                  lstLog.SelectedIndex = lstLog.SelectedIndex - 1;

               e.Handled = true;
               break;

            case Keys.Down:
               if (lstLog.SelectedIndex < lstLog.Items.Count - 1)
                  lstLog.SelectedIndex = lstLog.SelectedIndex + 1;

               e.Handled = true;
               break;
         }
      }

      private void lstLog_DrawItem(object sender, DrawItemEventArgs e)
      {
         // a nice piece of code from http://www.msdner.com/dev-archive/70/2-8-707629.shtm
         SizeF stringSize = e.Graphics.MeasureString(lstLog.Items[e.Index].ToString(), e.Font);

         // Draw the current item text based on the current Font and the custom brush settings.
         e.Graphics.DrawString(lstLog.Items[e.Index].ToString(), e.Font, Brushes.Black
            , new PointF(e.Bounds.Right - stringSize.Width, e.Bounds.Y));

         e.DrawFocusRectangle(); // If the ListBox has focus, draw a focus rectangle around the selected item.
      }

   }
}