RegEx

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace RegEx
{
    class Program
    {
        static void Main(string[] args)
        {
            string email = "ivan@abvbg";
            string regex = @"^[a-zA-Z_0-9]+@[a-zA-Z]+\.[a-z]{2,3}$";
            Match m = Regex.Match(email, regex);
            if (m.Success)
            {
                Console.WriteLine("Valid email!");
            }
            else
            {
                Console.WriteLine("Invalid email!");
            }
            /*string doc = "Smith's number: 0898880022\nFranky can be " +
      " found at 0888445566.\nSteven’ mobile number: 0887654321";

            string replacedDoc = Regex.Replace(doc, "(08)[0-9]{8}", "$1********");
            Console.WriteLine(replacedDoc);*/

            /*string pattern = @"\b[M]\w+";
            Regex rg = new Regex(pattern);
            string authors = "Mahesh Chand, Raj Kumar, Mike Gold, Allen O'Neill, Marshal Troll";
            MatchCollection matchedAuthors = rg.Matches(authors);
            foreach (var item in matchedAuthors)
            {
                Console.WriteLine(item);
            }*/
        }
    }
}