Add two numbers without using + operator

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 Addition_two_numbers_without_plus
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void btn_Addition_Click(object sender, EventArgs e)
{
int value1, value2;
if (!int.TryParse(textBox1.Text, out value1))
{
MessageBox.Show("Not a valid integer. Please re-enter.");
textBox1.Focus();
return;
}

if (!int.TryParse(textBox2.Text, out value2))
{
MessageBox.Show("Not a valid integer. Please re-enter.");
textBox2.Focus();
return;
}

MessageBox.Show("Addition:" + addition(Convert.ToInt32(textBox1.Text), Convert.ToInt32(textBox2.Text)).ToString());
clear();
}
void clear()
{
textBox1.Text = "";
textBox2.Text = "";
}
private int addition(int a, int b)
{

int result = 0, carry;
carry = a & b;

if (Convert.ToBoolean(carry))
{
result = a ^ b;
carry = carry << 1;
result = addition(carry, result);
}
else
{
result = a ^ b;
}

return result;

}
}
}