ASP.Net Error: The name 'price' does not exist in the current context

You need to declare the string variable outside of if condition.

protected void ImageButton2_Click1(object sender, ImageClickEventArgs e)
    {
        string price = string.Empty;
        if (TextBox1.Text != "0")
        {
            price = RadioButton2.Checked ? TextBox1.Text : "";
        }
        else {
            price = TextBox1.Text = "";
         
        }
        
        int data1 = Convert.ToInt32(Request.QueryString["id"].ToString());
        SqlCommand _cmd = new SqlCommand("editproduct1", _cn);
        _cmd.CommandType = CommandType.StoredProcedure;
        _cn.Open();
        _cmd.Parameters.AddWithValue("@ID", data1);
        _cmd.Parameters.AddWithValue("@Name", txtname.Text);     _cmd.Parameters.AddWithValue("@Description", elm1.Text);
        _cmd.Parameters.AddWithValue("@Price", price);
	_cmd.ExecuteNonQuery();
        Session["Message"] = true;
        Response.Redirect(Request.Url.AbsoluteUri);
        _cn.Close();
}

 Now price variable will be available for complete Button Click event.