// 
using System.Windows.Forms; 
using NCalc; 
// 
  string resText; 
  bool eqPressed; 
  double result; 
 
public void btnEqual_Click(object sender, EventArgs e) 
    { 
      Expression ex = new Expression(textBox1.Text); 
      if (ex.HasErrors()) 
      { 
        //Invalid Expression 
      } 
      else 
      { 
        result = Convert.ToDouble(ex.Evaluate()); 
        resText = result.ToString(); 
      } 
      textBox1.Text = resText; 
      text = resText; 
      eqPressed = true; 
 
    } 
// 

using System.Windows.Forms; 
 
class CalDrop : ToolStripDropDown 
  { 
   Control content; 
   ToolStripControlHost drop; 
 
public CalDrop(CalculatorControl content) 
    { 
 
      this.content = content; 
 
      this.drop= new System.Windows.Forms.ToolStripControlHost(content); 
 
      //Add the host to the list 
      this.Items.Add(this.drop); 
    } 
} 

private void button1_Click(object sender, EventArgs e) 
    { 
      CalculatorControl calculator = new CalculatorControl(); 
      CalDrop cal = new CalDrop(calculator); 
 
      Point controlLoc = fm.PointToScreen(button1.Location); 
      Point relativeLoc = new Point(controlLoc.X + button1.Width + 100, 
  controlLoc.Y + button1.Height * 2); 
      Rectangle calRect = button1.DisplayRectangle; 
      cal.Show(locPoint); 
    } 

private CalculatorPick calculator; 
 
public form1() 
{ 
      calculator = new CalculatorPick(); 
 
      calculator.Visible = false; 
      dataGridView2.Controls.Add(calculator); 
} 
 
private void dataGridView2_CellClick(object sender, DataGridViewCellEventArgs e) 
{ 
        if (e.ColumnIndex == clmCommision.Index) 
        { 
          Rectangle calRect = dataGridView2.GetCellDisplayRectangle 
   (e.ColumnIndex, e.RowIndex,false);          
 
          Point p = calculator.FindForm().PointToClient 
  (calculator.Parent.PointToScreen(calculator.Location)); 
          p.X -= calculator.Width/3; 
          p.Y += calculator.Height; 
          calculator.LocPoint = p; 
 
          calculator.Width = calRect.Width/3; 
          calculator.Height = calRect.Height; 
 
          calculator.Visible = true; 
          calculator.Calculator.btnEqual.Click += new EventHandler(calculatorBtnEqlClicked); 
        } 
        else 
          if(calculator!=null) 
          calculator.Visible = false; 
} 
 
void calculatorBtnEqlClicked(object sender, EventArgs e) 
{      
      dataGridView2.CurrentCell.Value = calculator.Calculator.Result.ToString();      
}