Par o Impar mediante procedimiento

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

namespace numero18
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
//Variables
int numero;
string resultado = "";

private void button2_Click(object sender, EventArgs e)
{
Application.Exit();
}
//Entrada
private void textBox1_TextChanged(object sender, EventArgs e)
{
numero = int.Parse(textBox1.Text);
}
//Proceso




private static void ParImpar(int numero, ref string salida)
{
//Variables
string r = "";
if (numero % 2 == 0)
{
r = "PAR";
}
else
{
r = "IMPAR";
}
salida = r;
}

private void button1_Click(object sender, EventArgs e)
{
ParImpar(numero, ref resultado);
//Salida
textBox2.Text = resultado.ToString();
}
}
}