Cách dùng DateTimePicker - MonthCalendar trong C# (winforms)

private void txtHoTen_KeyPress(object sender, KeyPressEventArgs e)
    {
       if (!((e.KeyChar >= 'a' && e.KeyChar <= 'z') ||(e.KeyChar == ' ')|| (e.KeyChar >= 'A' && e.KeyChar <= 'Z') || e.KeyChar == (char)8))
       e.Handled = true;
    }

private void txtSDT_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!(e.KeyChar >= '0' && e.KeyChar <= '9' || e.KeyChar == (char)8))
          e.Handled = true;
    }

private void Form1_Load(object sender, EventArgs e)
    {
       dateTimePicker1.MinDate = DateTime.Now;
       int dayofmonth = DateTime.DaysInMonth(DateTime.Now.Year, DateTime.Now.Month);
       dateTimePicker1.MaxDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, dayofmonth);
    }

private void btnDangKy_Click(object sender, EventArgs e)
    {
        if (string.IsNullOrEmpty(txtHoTen.Text) || string.IsNullOrEmpty(txtSDT.Text) || string.IsNullOrEmpty(txtEmail.Text))
        {
            MessageBox.Show("Bạn chưa nhập đầy đủ thông tin");
        }
        else if (!string.IsNullOrEmpty(txtHoTen.Text) || !string.IsNullOrEmpty(txtSDT.Text) || !string.IsNullOrEmpty(txtEmail.Text) == true)
        {
            MessageBox.Show("Chúc mừng bạn: " + txtHoTen.Text + "\nSố Điện Thoại: " + txtSDT.Text + "\nEmail: " + txtEmail.Text + "\nThời gian lựa chọn: " + dateTimePicker1.Value.ToShortDateString());
        }
    }

private void bntThoat_Click(object sender, EventArgs e)
    {
        Application.Exit();        
    }

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 Cau5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        
    private void btnDangKy_Click(object sender, EventArgs e)
    {
        if (string.IsNullOrEmpty(txtHoTen.Text) || string.IsNullOrEmpty(txtSDT.Text) || string.IsNullOrEmpty(txtEmail.Text))
        {
            MessageBox.Show("Bạn chưa nhập đầy đủ thông tin");
        }
        else if (!string.IsNullOrEmpty(txtHoTen.Text) || !string.IsNullOrEmpty(txtSDT.Text) || !string.IsNullOrEmpty(txtEmail.Text) == true)
        {
            MessageBox.Show("Chúc mừng bạn: " + txtHoTen.Text + "\nSố Điện Thoại: " + txtSDT.Text + "\nEmail: " + txtEmail.Text + "\nThời gian lựa chọn: " + dateTimePicker1.Value.ToShortDateString());
        }
    }


    private void txtHoTen_KeyPress(object sender, KeyPressEventArgs e)
    {
       if (!((e.KeyChar >= 'a' && e.KeyChar <= 'z') ||(e.KeyChar == ' ')|| (e.KeyChar >= 'A' && e.KeyChar <= 'Z') || e.KeyChar == (char)8))
       e.Handled = true;
    }

    private void txtSDT_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!(e.KeyChar >= '0' && e.KeyChar <= '9' || e.KeyChar == (char)8))
          e.Handled = true;
    }
   

    private void Form1_Load(object sender, EventArgs e)
      {
         dateTimePicker1.MinDate = DateTime.Now;
         int dayofmonth = DateTime.DaysInMonth(DateTime.Now.Year, DateTime.Now.Month);
         dateTimePicker1.MaxDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, dayofmonth);
      }

    private void bntThoat_Click(object sender, EventArgs e)
    {
        Application.Exit();        
    }
  }
}

private void btnHienthi_Click(object sender, EventArgs e)
    {
        txtStart.Text = monthCalendar1.SelectionStart.ToShortDateString();
        txtEnd.Text = monthCalendar1.SelectionEnd.ToShortDateString();
        txtmin.Text = monthCalendar1.MinDate.ToShortDateString();
        txtMax.Text = monthCalendar1.MaxDate.ToShortDateString();
        txtDayDate.Text = monthCalendar1.TodayDate.ToShortDateString();
    }

private void btnCountday_Click(object sender, EventArgs e)
    {
        int numdays;
        numdays = Convert.ToInt32((monthCalendar1.SelectionEnd - monthCalendar1.SelectionStart).TotalDays);
        txtday.Text = numdays.ToString();
    }

private void btnCountHour_Click(object sender, EventArgs e)
    {
        int numhour;
        numhour = Convert.ToInt32((monthCalendar1.SelectionEnd - monthCalendar1.SelectionStart).TotalHours);
        txthour.Text = numhour.ToString();
    }

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 Cau2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

    private void btnHienthi_Click(object sender, EventArgs e)
    {
        txtStart.Text = monthCalendar1.SelectionStart.ToShortDateString();
        txtEnd.Text = monthCalendar1.SelectionEnd.ToShortDateString();
        txtmin.Text = monthCalendar1.MinDate.ToShortDateString();
        txtMax.Text = monthCalendar1.MaxDate.ToShortDateString();
        txtDayDate.Text = monthCalendar1.TodayDate.ToShortDateString();
    }

    private void btnCountday_Click(object sender, EventArgs e)
    {
        int numdays;
        numdays = Convert.ToInt32((monthCalendar1.SelectionEnd - monthCalendar1.SelectionStart).TotalDays);
        txtday.Text = numdays.ToString();
    }

    private void btnCountHour_Click(object sender, EventArgs e)
    {
        int numhour;
        numhour = Convert.ToInt32((monthCalendar1.SelectionEnd - monthCalendar1.SelectionStart).TotalHours);
        txthour.Text = numhour.ToString();
    }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}