How to validation for combox in windows applications

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 WindowsFormsApplication1
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            foreach (Control cnt in this.Controls)
            {
               
               if (cnt is ComboBox)
                {
                    ComboBox cmb = (ComboBox)cnt;
                    if (cmb.SelectedItem == null)
                    {
                       
                     
                        errorProvider1.SetError(cmb, "Combox is not Selected");
                        cnt.BackColor = Color.Plum;
                    }
                }
            }
        }

        private void Form3_Load(object sender, EventArgs e)
        {
            comboBox1.Items.Add("a");
           
        }
    }
}

Hi Nayak

         But i need based on the ErrorProvider Control in windows applications.