format.cs

using System;
using System.Collections.Generic;
using System.Globalization;

// CultureInfo culture = new CultureInfo("en-US");

// Full-date notation as defined by RFC 3339, section 5.6, for example, 2024-03-28
string date1 = string.Format("{0:yyyy}-{0:MM}-{0:dd}", DateTime.Now);
Console.WriteLine(date1);

// RFC 3339, section 5.6, for example, 2024-03-28T17:32:28Z
string date2 = string.Format("{0:yyyy}-{0:MM}-{0:dd}T{0:hh}:{0:mm}:{0:ss}Z", DateTime.Now);
Console.WriteLine(date2);

// Curreny format CHF
NumberFormatInfo info = (NumberFormatInfo)CultureInfo.InvariantCulture.NumberFormat.Clone();
info.NumberGroupSeparator = "'";
info.NumberDecimalSeparator = ".";

// 2'147'483'647.00
Console.WriteLine(int.MaxValue.ToString("n", info));

// 123'456'789.12
Console.WriteLine(123456789.12.ToString("n", info));