System Test in Interview on ListBox

In this blog I am explaining how to deal some basic operations with Listbox and how to use classes and inheritance.

This blog explains -

• How to use classes and inheritance.
• CRUD operations with listbox using databse.
• How to use split function.
• How to validate the textboxes using javascript.
  

It also covers the the following System Test question,

1. Create a class for the math ( "+","-") operations -- name the class "MathOp".
2. Extend the class using inheritance to include ("*","/") name the class "MathOp2".
3. Create the following class/function when select a line from the list box, the user should be able to modify the values/operations and save it to the listbox/database Let’s say the user clicked on “1+3=4” , the values 1,3 should be displayed in the input text boxes. 

Step 1: At DataBase.

I use the following table to demonstrate the above concepts.

Create table MathRresults(
ID int primary key identity(1,1),
Result varchar(20)
)

Application

Step 2: Creating the project.

Now create the project using the following.

Go to Start, then All Programs and click Microsoft Visual Studio 2010.

Go to File, then click New, Project..., Visual C# , Web. Then select ASP.NET Empty Web Application.

Provide the project a name and specify the location.

 

Step 3 : Web.Config.

Create the connection string in the Web.Config file as in the following code snippet:

<connectionStrings>
    <add name="conStr"
    connectionString="Password= 1234; User ID=sa; Database=DB_Jai; Data Source=."
    providerName="System.Data.SqlClient"/>
</connectionStrings>

Next: Right-click on Solution Explorer and add a web form to your project. 

 

Make your .aspx as follows -



Step 4 : JavaScript Validations.

Use the following code to validate the textboxes.

< script type = "text/javascript" > function Valid()
{
    if (document.getElementById('<%=txtFirstNumber.ClientID%>').value.trim() == "") {
        var msg = document.getElementById('<%=lblMsg.ClientID %>');
        msg.innerHTML = "Please enter First Number";
        msg.style.color = "red";
        document.getElementById('<%=txtFirstNumber.ClientID%>').focus();
        return false;
    }
    if (document.getElementById('<%=txtSecondNumber.ClientID%>').value.trim() == "") {
        var msg = document.getElementById('<%=lblMsg.ClientID %>');
        msg.innerHTML = "Please enter Second Number";
        msg.style.color = "red";
        document.getElementById('<%=txtSecondNumber.ClientID%>').focus();
        return false;
    }
}
< /script>

CodeBehind

 

Add the following namespaces:

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

Invoke the ConnectionString from Web.Config as in the following:

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConStr"].ConnectionString);

Step 5 : Declare global variables.

private Decimal Num1;
private Decimal Num2;
string constr = ConfigurationManager.ConnectionStrings["connectionStr"].ConnectionString;

Step 6: Classes and Inheritance.

MathOp class Contains two methods that are Add, Subtract.

MathOp2 class Contains two methods that are Mul, Div.

public class MathOp
{
    public Decimal Add(Decimal value1, Decimal value2)
    {
        return (value1 + value2);
    }
    public Decimal Subtract(Decimal value1, Decimal value2)
    {
        return (value1 - value2);
    }
}
public class MathOp2: MathOp
{
    public Decimal Mul(Decimal value1, Decimal value2)
    {
        return (value1 * value2);
    }
    public Decimal Div(Decimal value1, Decimal value2)
    {
        return (value1 / value2);
    }
}

Step 7: User defined methods.

//Clear () method is used to clear the textbox box values.

private void Clear()
{
   txtFirstNumber.Text = string.Empty;
   txtSecondNumber.Text = string.Empty;
   lblResult.Text = string.Empty;
   lblMsg.Text = string.Empty;
}

//saveResult() method is used to save the result sets in database.

private void saveResult()
{
    SqlConnection con = new SqlConnection(constr);
    SqlCommand cmd = new SqlCommand("insert into MathRresults values('" + lblResult.Text + "')", con);
    SqlDataReader dbr;
    try
    {
        con.Open();
        dbr = cmd.ExecuteReader();
        lblMsg.Text = "Values saved Successfully";
        lblMsg.ForeColor = Color.Green;
        dbr.Read();

    }
    catch (Exception ex)
    {
        lblMsg.Text = "Failed to Save because :" + ex;
        lblMsg.ForeColor = Color.Red;
    }
    con.Close();
    BindResultsToListview();
}

// UpdateResult() method is used to update the result sets with existing records in database.

private void UpdateResult()
{
    int ? id = null;
    foreach(ListItem li in ListBox1.Items)
    {
        if (li.Selected == true)
        {
            id = Convert.ToInt32(ListBox1.SelectedValue);
        }
    }
    SqlConnection con = new SqlConnection(constr);
    SqlCommand cmd = new SqlCommand("Update MathRresults set Result = '" + lblResult.Text + "' Where ID = '" + id + "'", con);
    SqlDataReader dbr;
    try
    {
        con.Open();
        dbr = cmd.ExecuteReader();
        lblMsg.Text = "Values Updated Successfully";
        lblMsg.ForeColor = Color.Green;
        dbr.Read();
        //while (dbr.Read())
        //{
        //}
    }
    catch (Exception ex)
    {
        lblMsg.Text = "Failed to update because:" + ex;
        lblMsg.ForeColor = Color.Red;
    }
    finally
    {
        con.Close();
        BindResultsToListview();
    }
}

//BindResultsToListview Method is used to bind the operations to ListBox.

private void BindResultsToListview()
{
    Clear();
    SqlConnection con = new SqlConnection(constr);
    string cmd = "Select Id, Result from MathRresults";
    SqlDataAdapter adpt = new SqlDataAdapter(cmd, con);
    DataSet ds = new DataSet();
    adpt.Fill(ds, "MathRresults");
    DataTable myDataTable = ds.Tables[0];
    if (ds.Tables.Count > 0 && ds != null && ds.Tables[0].Rows.Count > 0) {
        ListBox1.DataSource = ds;
        ListBox1.DataValueField = "ID";
        ListBox1.DataTextField = "Result";
        ListBox1.DataBind();
    }
}

//DeleteFromListView is used to delete the selected item in ListBox.

private int DeleteFromListView(int id)
{
    //Here using statement is automatically close the connections
    using(SqlConnection con = new SqlConnection(constr))
    {
        SqlCommand cmd = new SqlCommand("delete from MathRresults where id = " + id + "", con);
        con.Open();
        cmd.ExecuteNonQuery();
        return 0;
    }
}

Step 8 : Page load.

Copy the following code in page_ load. 

if (!Page.IsPostBack)
{
   BindResultsToListview();
}

Clear();

//txtFirstNumber value to be assigned to Num1 variable.
    Num1 = Convert.ToDecimal(txtFirstNumber.Text);
//txtSecondNumber value to be assigned to Num2 variable.
    Num2 = Convert.ToDecimal(txtSecondNumber.Text);

Step 9: Addition.

To add or update two values and save the result set in database –

protected void btnAdd_Click(object sender, EventArgs e)
{
    MathOp2 m = new MathOp2();
    Decimal additon = m.Add(Num1, Num2);
    lblResult.Text = (Num1 + ("+" + (Num2 + ("=" + additon))));
    lblResult.ForeColor = Color.Green;

    //this is pretty simple
    //if your not selected any item in listbox it's save your result as a new record in database.
    //if your selected any item in listbox it's update your result with existing record in database.

    if (ListBox1.SelectedValue == string.Empty)
    {
        saveResult();
    }
    else
    {
        UpdateResult();
    }
}

Step 10: Subtraction.

To Subract values and save the result set in database –

protected void btnSubtract_Click(object sender, EventArgs e)
{
    MathOp2 m = new MathOp2();
    Decimal subtraction = m.Subtract(Num1, Num2);
    lblResult.Text = (Num1 + ("-" + (Num2 + ("=" + subtraction))));
    lblResult.ForeColor = Color.Green;
    if (ListBox1.SelectedValue == string.Empty) saveResult();
    else UpdateResult();
}

Step 11: Multiplication.

To multipliy two values and save the result set in database -

protected void btnMultiply_Click(object sender, EventArgs e)
{
    MathOp2 m = new MathOp2();
    Decimal division = m.Mul(Num1, Num2);
    lblResult.Text = (Num1 + ("*" + (Num2 + ("=" + division))));
    lblResult.ForeColor = Color.Green;
    if (ListBox1.SelectedValue == string.Empty) saveResult();
    else UpdateResult();
}

Step 12 : Division.

For division of two values and save the result set in database -

protected void btnDivide_Click(object sender, EventArgs e)
{
    // if txtSecondNumber value is zero, then the result would be infinite.
    // To prevent that make one alert for user that "Divide By Zero is Invalid"
    if (Num2 == 0)
    {
        lblMsg.Text = "Divide By Zero is Invalid";
        lblMsg.ForeColor = Color.Red;
        return;
    }
    MathOp2 m = new MathOp2();
    Decimal division = m.Div(Num1, Num2);
    lblResult.Text = (Num1 + ("/" + (Num2 + ("=" + division))));
    lblResult.ForeColor = Color.Green;
    if (ListBox1.SelectedValue == string.Empty) saveResult();
    else UpdateResult();
}

Step 13 : Delete the selected listbox value.

To delete the selected item from listbox as well as database –

protected void btnDelete_Click(object sender, EventArgs e)
{
    lblResult.Text = string.Empty;
    lblMsg.Text = string.Empty;
    for (int i = 0; i <= ListBox1.Items.Count - 1; i++)
    {
        if (ListBox1.Items[i].Selected != false)
        {
            DeleteFromListView(Convert.ToInt32(ListBox1.Items[i].Value));
        }
    }
    ListBox1.Items.Clear();
    BindResultsToListview();
    lblMsg.Text = "Selected Value deleted successfully";
}

// ListBox1_SelectedIndexChanged

protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    lblMsg.Text = string.Empty;
    if (ListBox1.SelectedValue == string.Empty)
    {
        return;
    }
    int ? id = null;
    string selectedtext = null;
    foreach(ListItem li in ListBox1.Items)
    {
        if (li.Selected == true)
        {
            id = Convert.ToInt32(ListBox1.SelectedValue);
        }
    }

    SqlConnection con = new SqlConnection(constr);
    SqlDataAdapter adpt = new SqlDataAdapter("Select * from MathRresults Where Id = '" + id + "'", con);
    DataSet ds = new DataSet();
    adpt.Fill(ds, "MathRresults");
    DataTable myDataTable = ds.Tables[0];

    if (ds.Tables.Count > 0 && ds != null && ds.Tables[0].Rows.Count > 0)
    {
        selectedtext = ds.Tables[0].Rows[0]["Result"].ToString();
    }

    //Split the item by the operator and the '=' into an array of strings

    string[] parts = selectedtext.Split('+', '-', '*', '/', '=');
    if (parts.Length > 2) {
        //Define a variable for each part
        string part1 = parts[0].Trim();
        string part2 = parts[1].Trim();
        string part3 = parts[2].Trim();
        txtFirstNumber.Text = part1;
        txtSecondNumber.Text = part2;
        lblResult.Text = part3;
    }
}

I hope you enjoyed it.