Increment Decrement TextBox value on plus minus Button Click using C# and VB.Net

Hi tareq16278,

please refer below sample.

HTML

<asp:Button ID="btnMinus" runat="server" OnClick="OnMinus"
    Style="font-weight: 700; font-size: x-large" Text="-" />
<asp:TextBox ID="txtNumber" runat="server" Width="49px"></asp:TextBox>
<asp:Button ID="btnPlus" runat="server" OnClick="OnPlus"
    Style="font-size: x-large" Text="+" />

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        txtNumber.Text = "1";
    }
}

protected void OnMinus(object sender, EventArgs e)
{
    if (int.Parse(txtNumber.Text) > 0)
    {
        txtNumber.Text = (int.Parse(txtNumber.Text) - 1).ToString();
    }
}

protected void OnPlus(object sender, EventArgs e)
{
    txtNumber.Text = (int.Parse(txtNumber.Text) + 1).ToString();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        txtNumber.Text = "1"
    End If
End Sub

Protected Sub OnMinus(ByVal sender As Object, ByVal e As EventArgs)
    If Integer.Parse(txtNumber.Text) > 0 Then
        txtNumber.Text = (Integer.Parse(txtNumber.Text) - 1).ToString()
    End If
End Sub

Protected Sub OnPlus(ByVal sender As Object, ByVal e As EventArgs)
    txtNumber.Text = (Integer.Parse(txtNumber.Text) + 1).ToString()
End Sub

Screenshot