Microsoft Visual C# Example Application: The Standard Deviation

The factors in these equations are:

1. Start Microsoft Visual Studio
2. To create a new application, on the main menu, click File -> New Project...
3. In the middle list, click Windows Forms Application
4. Change the Name to StandardDeviation2
5. Click OK
6. In the Solution Explorer, right-click Form1.cs and click Rename
7. Type Exercise.cs and press Enter
8. Design the form as follows:
    

   Control Name Text Label   Value: TextBox txtValue   Button btnAdd Add ListBox lbxValues   Button btnClear Clear Label   Standard Deviation: TextBox txtStandard Deviation   Button btnClose Close

9. Double-click an unoccupied area of the form
10. Change the file as follows:

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    
    namespace MeasuresOfCenter
    {
        public partial class Measures : Form
        {
            List<double> values;
    
            public Measures()
            {
                InitializeComponent();
            }
    
            private void Measures_Load(object sender, EventArgs e)
            {
                values = new List<double>();
            }
    
            void ShowValues()
            {
                lbxValues.Items.Clear();
    
                for (int i = 0; i < values.Count; i++)
                    lbxValues.Items.Add(values[i]);
            }
        }
    }

11. Return to the form
12. Double-click the Add button
13. Implement the event as follows:

    private void btnAdd_Click(object sender, EventArgs e)
    {
        // This the value that will be added to the text box
        double value = 0.00;
        double sum = 0.00, sumSquares = 0.00, squareSums;
        double stdDev = 0.00;
    
        // Check that the user entered a value in the text box
        if (txtValue.Text.Length == 0)
        {
            MessageBox.Show("You must enter a value.", "Standard Deviation");
            return;
        }
    
        try
        {
            // Get the value the user entered
            value = double.Parse(txtValue.Text);
            // Add it to the collection
            values.Add(value);
            // Show the values in the list box
            ShowValues();
    
            txtValue.Text = "";
            txtValue.Focus();
        }
        catch (FormatException)
        {
            MessageBox.Show("The value you entered is invalid.",
                            "Standard Deviation");
        }
    
        // Calculate the total for the sum
        for (int i = 0; i < values.Count; i++)
            sum += values[i];
        squareSums = sum * sum;
        for (int i = 0; i < values.Count; i++)
            sumSquares += (values[i] * values[i]);
    
        // Now we can calculate the standard deviation
        double numerator = values.Count * sumSquares - squareSums;
        double denominator = values.Count * (values.Count - 1);
        stdDev = Math.Sqrt(numerator / denominator);
    
        // Display the values(standard deviationand stuff)
        txtCount.Text = values.Count.ToString();
        txtSum.Text = sum.ToString("F");
        txtSumSquares.Text = sumSquares.ToString("F");
        txtSquareSums.Text = squareSums.ToString("F");
        txtStandardDeviation.Text = stdDev.ToString("F");
    }

14. Return to the form
15. To execute, press F5
16. Enter a few values and click Add after each
     
    
17. Close the form and return to your programming environment
18. Double-click the Clear button
19. Implement its event as follows:

    private void btnClear_Click(object sender, EventArgs e)
    {
        values.Clear();
        lbxValues.Items.Clear();
    
        txtValue.Text = "";
        txtCount.Text = "";
        txtSum.Text = "";
        txtMean.Text = "";
        txtStandardDeviation.Text = "";
        txtValue.Focus();
    }

20. Return to the form
21. To execute, press F5
22. Enter a few values and click Add after each
     
    
    
23. Click Clear
24. Close the form and return to your programming environment
25. Double-click the Close button
26. Implement the event as follows:

    private void btnClose_Click(object sender, EventArgs e)
    {
        Close();
    }

27. To execute, press F5
28. Enter a few values and click Add after each
     
    
    
29. Close the form and return to your programming environment

Application