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CSharp · Console

/Program.cs

using System;
using System.Globalization;
					
public class Program
{
	public static void Main()
	{
		var ni = new CultureInfo(CultureInfo.CurrentCulture.Name).NumberFormat;
		
		ni.NumberDecimalDigits = 0;     //Keep the ".00" from appearing
		ni.NumberGroupSeparator = " ";  //Set the group separator to a space
		ni.NumberGroupSizes = new int[] { 3 };  //Groups of 3 digits
		var dig = 123456789;
		
		Console.WriteLine(dig.ToString("N", ni));
	}
}