CRUD Using Parameter

<form id="form1" runat="server">
<div>
<h1>Registration Form</h1>
<asp:Label ID="lblId" runat="server" Visible="false" ></asp:Label>
<table style="font-size:18px">
<tr>
    <td> Name</td>
    <td><asp:TextBox ID="txtName" runat="server"></asp:TextBox></td>
</tr>
<tr>
    <td>Subject:</td>
    <td><asp:DropDownList ID="ddlSub" runat="server">
        <asp:ListItem>--Select Subjects-- </asp:ListItem>
        <asp:ListItem Value="1">Physics </asp:ListItem>
        <asp:ListItem Value="2">Chemistry </asp:ListItem>
        <asp:ListItem Value="3">Biology </asp:ListItem>
        <asp:ListItem Value="4">Maths </asp:ListItem>
        <asp:ListItem Value="5">English </asp:ListItem>
        <asp:ListItem Value="6">Computer </asp:ListItem>
        <asp:ListItem Value="7">History & Civics </asp:ListItem>
        </asp:DropDownList></td>
</tr>
<tr>
    <td>Email:</td>
    <td><asp:TextBox ID="txtEmail" runat="server"></asp:TextBox></td>
    </tr>
<tr>
    <td>Gender:</td>
    <td>
        <asp:RadioButtonList ID="rbtnListGender" runat="server" RepeatDirection="Horizontal">
            <asp:ListItem Text="Male" Value="Male"></asp:ListItem>
            <asp:ListItem Text="Female" Value="Female"></asp:ListItem>
        </asp:RadioButtonList>
    </td>
</tr>
<tr>
    <td></td>
    <td>
        <asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" />
        <asp:Button ID="btnUpdate" runat="server" Text="Update" OnClick="btnUpdate_Click" Visible="false" />
        <asp:Button ID="btnClear" runat="server" Text="Clear" OnClick="btnClear_Click" />
    </td>
</tr>
</table>
<h2>Registration Data</h2>
<table border="1" style="border-collapse:collapse">
<tr >
    <th>Name</th>
    <th>Email</th>
    <th>Gender</th>
    <th>Subject</th>
    <th colspan="2">Action</th>
</tr>
<asp:Repeater ID="rptStudents" runat="server" OnItemCommand="rptStudents_ItemCommand">
    <ItemTemplate>
      <tr>
        <td><%# Eval("Name") %></td>
        <td><%# Eval("Email") %></td>
        <td><%# Eval("Gender") %></td>
        <td><%# Eval("Subject") %></td>
        <td>
            <asp:LinkButton ID="lbtnEdit" runat="server" CommandName="Edit"
                    CommandArgument='<%# Eval("Id") %>'>Edit</asp:LinkButton>
        </td>
        <td>
            <asp:LinkButton ID="lbtnDelete" runat="server" CommandName="Delete"
                        CommandArgument='<%# Eval("Id") %>'>Delete</asp:LinkButton>
        </td>
      </tr>
    </ItemTemplate>
</asp:Repeater>
</table>
</div>
</form>

SqlConnection con = new SqlConnection(@"Data Source= ; Initial Catalog= ; User ID= ; Password= ");

protected void Page_Load(object sender, EventArgs e)
{
  if (!IsPostBack)
   {
      bindStudents();
   }
}

protected void btnSave_Click(object sender, EventArgs e)
{
    SqlCommand cmd = new SqlCommand("INSERT INTO tblStudents (Name, Gender, Email, SubjectId
                                    VALUES" +" (@Name, @Gender, @Email, @SubjectId)", sqlConn);

    cmd.Parameters.AddWithValue("@Name", txtName.Text);
    cmd.Parameters.AddWithValue("@Gender", rbtnListGender.SelectedValue);
    cmd.Parameters.AddWithValue("@Email", txtEmail.Text);
    cmd.Parameters.AddWithValue("@SubjectId", ddlSub.SelectedValue);
    sqlConn.Open();
    cmd.ExecuteNonQuery();
    sqlConn.Close();
    Response.Write("<script>alert('Data Saved Successfully')</script>");
    bindStudents();
    btnClear_Click(sender, e);
}

protected void rptStudents_ItemCommand(object source, RepeaterCommandEventArgs e)
{
if (e.CommandName == "Edit")
    { 
    SqlCommand cmd = new SqlCommand("SELECT * FROM tblStudents WHERE Id = @Id", sqlConn);
    cmd.Parameters.AddWithValue("@Id", e.CommandArgument);
    SqlDataAdapter da = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    da.Fill(dt); 
    lblId.Text = dt.Rows[0]["Id"].ToString();
    txtName.Text = dt.Rows[0]["Name"].ToString();
    txtEmail.Text = dt.Rows[0]["Email"].ToString();
    rbtnListGender.SelectedValue = dt.Rows[0]["Gender"].ToString();
    ddlSub.SelectedValue = dt.Rows[0]["SubjectId"].ToString();
    btnSave.Visible = false;
    btnUpdate.Visible = true;
    }
else if (e.CommandName == "Delete")
    {
                
    SqlCommand cmd = new SqlCommand("DELETE FROM tblStudents WHERE Id = @Id", sqlConn);
    cmd.Parameters.AddWithValue("@Id", e.CommandArgument);
    sqlConn.Open();
    cmd.ExecuteNonQuery();
    sqlConn.Close();
    Response.Write("<script>alert('Data Delete Successfully')</script>"); 
    bindStudents();
    }
}

protected void btnUpdate_Click(object sender, EventArgs e)
{
            
    SqlCommand cmd = new SqlCommand("UPDATE tblStudents SET Name = @Name, Gender = @Gender," +
                            " Email = @Email, SubjectId = @SubjectId WHERE Id = @Id", sqlConn);

    cmd.Parameters.AddWithValue("@Name", txtName.Text);
    cmd.Parameters.AddWithValue("@Gender", rbtnListGender.SelectedValue);
    cmd.Parameters.AddWithValue("@Email", txtEmail.Text);
    cmd.Parameters.AddWithValue("@SubjectId", ddlSub.SelectedValue);
    cmd.Parameters.AddWithValue("@Id", lblId.Text);
    sqlConn.Open();
    cmd.ExecuteNonQuery();
    sqlConn.Close();
    Response.Write("<script>alert('Data Update Successfully')</script>"); 
    bindStudents();
    btnClear_Click(sender, e);
}

protected void btnClear_Click(object sender, EventArgs e)
{
    lblId.Text = ""; txtName.Text = ""; txtEmail.Text = ""; rbtnListGender.ClearSelection();
    ddlSub.SelectedIndex = 0; btnSave.Visible = true; btnUpdate.Visible = false;
}

protected void bindStudents()
{ 
    SqlCommand cmd = new SqlCommand("SELECT st.Id, st.Name, st.Email, st.Gender, sub.Sub_Name AS Subject" +
                "FROM tblStudents st left outer JOIN MasterSubjects sub ON sub.Id = st.SubjectId", sqlConn);

    SqlDataAdapter da = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    da.Fill(dt); 
    rptStudents.DataSource = dt;
    rptStudents.DataBind();
}