Return part of a string in C# and VB.Net

Hi ShihabKhan,

Refer below sample.

HTML

Name : <asp:TextBox runat="server" ID="txtName" OnTextChanged="Display" AutoPostBack="true" />

Code

C#

protected void Display(object sender, EventArgs e)
{
    ScriptManager.RegisterStartupScript(this, this.GetType(), "Message", "alert('" + txtName.Text.Substring(0, 4) + "');", true);
}

VB.Net

Protected Sub Display(ByVal sender As Object, ByVal e As EventArgs)
    ScriptManager.RegisterStartupScript(Me, Me.GetType(), "Message", "alert('" & txtName.Text.Substring(0, 4) & "');", True)
End Sub

Screenshot