using System;

using System.Text.RegularExpressions;

using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(IsIntegerRegex("")); // false

        Console.WriteLine(IsIntegerRegex("2342342")); // true

        Console.WriteLine(IsInteger("1231231.12")); // false

        Console.WriteLine(IsInteger("1231231")); // true

        Console.WriteLine(IsInteger("1,231,231")); // true

    }

    private static bool IsIntegerRegex(string value)

    {

        const string regex = @"^\d+$";

        return Regex.IsMatch(value, regex);

    }

​

    private static bool IsInteger(string value)

    {

        var culture = CultureInfo.CurrentCulture;

        const NumberStyles style = 

            // NumberStyles.AllowDecimalPoint | 

            // NumberStyles.AllowTrailingWhite | 

            // NumberStyles.AllowLeadingWhite | 

            // NumberStyles.AllowLeadingSign |

            NumberStyles.AllowThousands;

        return Int64.TryParse(value, style, culture, out _);

    }

}