Convert Temperature in C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace tempreture
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double val1;
        double val2;
        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            double val1;
            val1 = double.Parse(textBox1.Text);
        }
        private double farhen()
        {
            double farenhiet;
            farenhiet = (val1 * 9 / 5) + 32;
            return farenhiet;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox2 = farhen(val2).ToString();
        }

        private void textBox3_TextChanged(object sender, EventArgs e)
        {
            double val2;
            val2 = double.Parse(textBox1.Text);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox2 = farhen(val2).ToString();
        }
        private double cels()
        {
            double cels;
            cels= (val2-32) * 5/ 9 ;
            return cels;
        }
        private void Form1_Load(object sender, EventArgs e)
        {
        }
    }
}