Calculate Sum of TextBoxes values on TextBox TextChanged event in ASP.Net

 Hi sanjoyp7er,

Please take reference the below code and correct your code.

HTML

First:
<asp:TextBox ID="txtFirst" runat="server" AutoPostBack="true" OnTextChanged="txtFirst_TextChanged"></asp:TextBox>
<br />
Second:
<asp:TextBox ID="txtSecond" runat="server"></asp:TextBox>

Code

C#

protected void txtFirst_TextChanged(object sender, EventArgs e)
{
    int first = Convert.ToInt32(txtFirst.Text.Trim() != string.Empty ? txtFirst.Text.Trim() : "0");
    int second = Convert.ToInt32(txtSecond.Text.Trim() != string.Empty ? txtSecond.Text.Trim() : "0");
    txtSecond.Text = (first + second).ToString();
}

Vb.Net

Protected Sub txtFirst_TextChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim first As Integer = Convert.ToInt32(If(txtFirst.Text.Trim() <> String.Empty, txtFirst.Text.Trim(), "0"))
    Dim second As Integer = Convert.ToInt32(If(txtSecond.Text.Trim() <> String.Empty, txtSecond.Text.Trim(), "0"))
    txtSecond.Text = (first + second).ToString()
End Sub

Screenshot