Count Number of Vowels in String (C# Source Code)

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 Vowel_Counter
{
    public partial class frmVowelCounter : Form
    {
        public frmVowelCounter()
        {
            InitializeComponent();
        }

        private void btnCount_Click(object sender, EventArgs b)
        {
            string text = txtText.Text;
            int my_count = 0;

            foreach (char ch_vowel in text)
            {
                switch (ch_vowel)
                {
                    case 'a':
                    case 'A':
                        my_count++;
                        break;
                    case 'e':
                    case 'E':
                        my_count++;
                        break;
                    case 'i':
                    case 'I':
                        my_count++;
                        break;
                    case 'o':
                    case 'O':
                        my_count++;
                        break;
                    case 'u':
                    case 'U':
                        my_count++;
                        break;
                    default:
                        break;
                }
            }

            if (text == "")
            {
                MessageBox.Show("There are 0 vowels. Please enter some text.");
            }

            else
            {
                MessageBox.Show("The number of vowels in " + text + " is " + my_count);
            }
        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}