using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        private double a, b;
        private bool isNumbers(ref double a, ref double b)
        {
            return Double.TryParse(tbLeft.Text, out a) && Double.TryParse(tbRight.Text, out b);
        }

        private void showErrorInput()
        {
            result.Text = "Ошибка ввода данных!";
        }
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void addition_Click(object sender, EventArgs e)
        {
            if (isNumbers(ref a, ref b))
            {
                result.Text = (a + b).ToString();
            }
            else
            {
                showErrorInput();
            }
        }

        protected void multiplication_Click(object sender, EventArgs e)
        {
            if (isNumbers(ref a, ref b))
            {
                result.Text = (a * b).ToString();
            }
            else
            {
                showErrorInput();
            }
        }

        protected void division_Click(object sender, EventArgs e)
        {
            if (isNumbers(ref a, ref b) && b!=0)
            {
                result.Text = (a / b).ToString();
            }
            else
            {
                showErrorInput();
            }
        }

        protected void subtraction_Click(object sender, EventArgs e)
        {
            if (isNumbers(ref a, ref b))
            {
                result.Text = (a - b).ToString();
            }
            else
            {
                showErrorInput();
            }
        }
    }
}