static void Main()
     {
        Application.Run( new FrmClassAverage() );
     }

     // handles Add Grade Button's Click event
     private void btnAdd_Click(
        object sender, System.EventArgs e )
     {
        // clear previous grades and calculation result
        if ( lblOutput.Text != "" )
        {
           lblOutput.Text = "";
           lstGrades.Items.Clear();
        }

        // display grade in ListBox
        lstGrades.Items.Add( Int32.Parse( txtInput.Text ) );
        txtInput.Clear(); // clear grade from TextBox
        txtInput.Focus(); // transfer focus to TextBox

        // prohibit users from entering more than 10 grades
        if ( lstGrades.Items.Count == 10 )
        {
           btnAdd.Enabled = false; // disable Add Grade Button
           btnAverage.Focus(); // transfer focus to Average Button
        }

     } // end method btnAdd_Click

     // handles Average Button's Click event
     private void btnAverage_Click(
        object sender, System.EventArgs e )
     {
        // initialization phase
        int intTotal = 0;
        int intGradeCounter = 0;
        int intGrade = 0;
        double dblAverage = 0;

        // sum grades in ListBox
        do
        {
           // read grade from ListBox
           intGrade = ( int )
              lstGrades.Items[ intGradeCounter ];
           intTotal += intGrade; // add grade to total
           intGradeCounter++; // increment counter
        } while ( intGradeCounter < 10 );

        dblAverage = intTotal / 10.0; // calculate average
        lblOutput.Text = String.Format( "{0:F}", dblAverage );
        btnAdd.Enabled = true; // enable Add Grade Button
        txtInput.Focus(); // reset focus to Enter grade: TextBox

     } // end method btnAverage_Click

  } // end class FrmClassAverage
}