C#

using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

//alias
using LangD = SA7.Cl_LangData;
using Gr = SA7.Cl_Graphics;
using Globals = SA7.Cl_Globals;

namespace SA7
{
  public partial class FormDateTime : Form
  {

    private bool FormDateTime_FirstShow = true;     // flag: first call to FormDateTime_Load

    Cl_DateTime Tempo = new Cl_DateTime();


    public struct SYSTEMTIME
    {
      public short wYear;
      public short wMonth;
      public short wDayOfWeek;
      public short wDay;
      public short wHour;
      public short wMinute;
      public short wSecond;
      public short wMilliseconds;
    }

    //functions to read and to set time
    [DllImport("coredll.dll")]
    private extern static void GetSystemTime(ref SYSTEMTIME lpSystemTime);

    [DllImport("coredll.dll")]
    private extern static uint SetSystemTime(ref SYSTEMTIME lpSystemTime);

    //---------------------------------------------------------------------------------

    public FormDateTime()
    {
      InitializeComponent();
      this.Location = new Point((800 - this.Width) / 2, (480 - this.Height) / 2);
    }
    //---------------------------------------------------------------------------------.

    private void FormDateTime_Load(object sender, EventArgs e)
    {
      if (FormDateTime_FirstShow) {

        FormDateTime_FirstShow = false;
      }

      CtrlsDesc();
      UpdateDateTime();
      ExitTr.Enabled = true;
    }
    //---------------------------------------------------------------------------------

    private void FormDateTime_Paint(object sender, PaintEventArgs e)
    {
      //draw window border
      Gr.DrawFrContour(e, 0, 1, 1, this.Width - 1, this.Height - 1);
    }
    //---------------------------------------------------------------------------------

    //update strings
    public void CtrlsDesc()
    {
      AbortBt.Text = FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinExit);
      UpdateBt.Text = FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinUpadateTime);
      DateLb.Text = FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinDate);
      TimeLb.Text = FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinTime);
      OKVBt.Text = FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinOK);
    }
    //---------------------------------------------------------------------------------

    // update controls with date and time
    private void UpdateDateTime()
    {
      DateTime tmp;

      tmp = DateTime.Now;
      DateRTB.Text = string.Format("{0:00} {1} {2}", tmp.Day, GetMonthStr(tmp.Month), tmp.Year);
      TimeRTB.Text = string.Format("{0:00}:{1:00}:{2:00}", tmp.Hour, tmp.Minute, tmp.Second);

      UpdateDate();
      UpdateTime();
    }
    //---------------------------------------------------------------------------------
    private void UpdateDate()
    {
      DateTime tmp;

      tmp = DateTime.Now;

      MonthCalendar.CurrentMonth = tmp;
      MonthCalendar.SelectedDate = tmp;
    }
    //---------------------------------------------------------------------------------
    private void UpdateTime()
    {
      DateTime tmp;

      tmp = DateTime.Now;

      ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[0]).SelectedIndex = tmp.Hour;
      ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[1]).SelectedIndex = tmp.Minute;
      ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[2]).SelectedIndex = tmp.Second;
    }
    //---------------------------------------------------------------------------------

    // get month in text format
    private string GetMonthStr(Int32 mese)
    {
      switch (mese)
      {
        case 1:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinGen);

        case 2:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinFeb);

        case 3:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinMaz);

        case 4:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinApr);

        case 5:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinMag);

        case 6:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinGiu);

        case 7:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinLug);

        case 8:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinAgo);

        case 9:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinSet);

        case 10:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinOtt);

        case 11:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinNov);

        case 12:
          return FormMain.LF.GetStr(LangD.LANG_Win, LangD.LANG_WinDic);

        default:
          break;
      }

      return "";
    }
    //---------------------------------------------------------------------------------

    //accept the changes
    private void UpdateBt_Click(object sender, EventArgs e)
    {
      DateTime tmp;

      ExitTr.Interval = Globals.EXIT_TR_TIME;

      // Call the native GetSystemTime method
      // with the defined structure.
      SYSTEMTIME systime = new SYSTEMTIME();
      GetSystemTime(ref systime);

      tmp = DateTime.Parse(string.Format("{0:00}/{1:00}/{2:00} {3:00}:{4:00}:{5:00}", MonthCalendar.SelectedDate.Month, MonthCalendar.SelectedDate.Day, MonthCalendar.SelectedDate.Year, ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[0]).SelectedIndex, ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[1]).SelectedIndex, ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[2]).SelectedIndex));
      tmp = tmp.ToUniversalTime();

      // Set the system clock
      systime.wDay = (short)tmp.Day;
      systime.wMonth = (short)tmp.Month;
      systime.wYear = (short)tmp.Year;
      systime.wHour = (short)tmp.Hour;
      systime.wMinute = (short)tmp.Minute;
      systime.wSecond = (short)tmp.Second;

      SetSystemTime(ref systime);

      // timer to close the form with a little delay to avoid the user
      // to push a button in the form below (touchscreen panel) 
      UpdateTr.Enabled = true;
    }
    //---------------------------------------------------------------------------------
    private void UpdateTr_Tick(object sender, EventArgs e)
    {
      UpdateTr.Enabled = false;
      Close();
    }
    //---------------------------------------------------------------------------------

    //close the windows
    private void AbortBt_Click(object sender, EventArgs e)
    {
      ExitTr.Enabled = false;
      Close();
    }
    //---------------------------------------------------------------------------------

    private void OKVBt_Click(object sender, EventArgs e)
    {
      ExitTr.Interval = Globals.EXIT_TR_TIME;
      
      TimeRTB.Text = string.Format("{0:00}:{1:00}:{2:00}", ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[0]).SelectedIndex, ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[1]).SelectedIndex, ((BeeMobile.iWheel.TextCylinder)TimeIW.Cylinders[2]).SelectedIndex);

      DateLb.Visible = true;
      TimeLb.Visible = true;
      DateRTB.Visible = true;
      TimeRTB.Visible = true;
      AbortBt.Visible = true;
      UpdateBt.Visible = true;
      MonthCalendar.Visible = false;
      TimeIW.Visible = false;
      OKVBt.Visible = false;
    }
    //---------------------------------------------------------------------------------

    //a date has been selected
    private void MonthCalendar_SelectedDateChanged(object sender, EventArgs e)
    {
      ExitTr.Interval = Globals.EXIT_TR_TIME;

      MonthCalendar.Visible = false;
      DateRTB.Text = String.Format("{0:00} {1} {2}", MonthCalendar.SelectedDate.Day, GetMonthStr(MonthCalendar.SelectedDate.Month), MonthCalendar.SelectedDate.Year);
      DateLb.Visible = true;
      TimeLb.Visible = true;
      DateRTB.Visible = true;
      AbortBt.Visible = true;
      UpdateBt.Visible = true;
      TimeIW.Visible = false;
      OKVBt.Visible = false;
      TimeRTB.Visible = true;
    }
    //---------------------------------------------------------------------------------

    //click on time
    private void TimeRTB_Click(object sender, EventArgs e)
    {
      ExitTr.Interval = Globals.EXIT_TR_TIME;

      // update the displayed time
      UpdateTime();
      DateLb.Visible = false;
      TimeLb.Visible = false;
      DateRTB.Visible = false;
      TimeRTB.Visible = false;
      AbortBt.Visible = false;
      UpdateBt.Visible = false;
      MonthCalendar.Visible = false;
      TimeIW.Visible = true;
      OKVBt.Visible = true;
    }
    //---------------------------------------------------------------------------------

    //click on date
    private void DateRTB_Click(object sender, EventArgs e)
    {
      ExitTr.Interval = Globals.EXIT_TR_TIME;
      
      // update the displayed date
      UpdateDate();
      DateLb.Visible = false;
      TimeLb.Visible = false;
      DateRTB.Visible = false;
      TimeRTB.Visible = false;
      AbortBt.Visible = false;
      UpdateBt.Visible = false;
      TimeIW.Visible = false;
      OKVBt.Visible = false;
      MonthCalendar.Visible = true;
    }
    //---------------------------------------------------------------------------------

    private void FormDateTime_Click(object sender, EventArgs e)
    {
      ExitTr.Interval = Globals.EXIT_TR_TIME;
    }
    //---------------------------------------------------------------------------------

    private void ExitTr_Tick(object sender, EventArgs e)
    {
      ExitTr.Enabled = false;
      Close();
    }
    //---------------------------------------------------------------------------------

  }
}

TranslateMessage function (winuser.h) | Microsoft Docs[^]:

The character messages are posted to the calling thread's message queue, to be read the next time the thread calls the GetMessage or PeekMessage function.

<PlatformTarget>AnyCPU</PlatformTarget>

Bernhard Hiller wrote:

But compiling for 64bit only could allow for more compiler optimizations (or am I mistaken?), so I'd prefer to create 64bit executables.

• Drop 32bit versions of dependencies and drop the release that uses them. Sounds like that's the plan.
• Write code that explicitly assumes pointers are 8 bytes (doesn't come up a lot in C# obviously, but you can do it).
• In 32bit mode, FP math gets done with x87 instructions, occasionally this required some workarounds to deal with 80bit/64bit precision mismatches, all of that nonsense can be removed. Most projects didn't bother with this in the first place.
• Boldly using System.Numerics.Vectors all over the place, which is fast (well, some parts of it are fast, definitely double check) in 64bit mode but worse than pointless in 32bit mode.
• Using things from System.Runtime.Intrinsics with X64 in the name, such as System.Runtime.Intrinsics.X86.Sse.X64, without checking IsSupported and without fallback.

var x = list.GroupBy(g => g.Key).Select(grp => grp.Skip(1)).SelectMany(i => i);

var x = list.GroupBy(g => g.Key).Select(grp =>
    grp.Count() == 1 
       ? grp 
       : grp.Skip(1)).SelectMany(i => i);