using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static readonly Regex PasswordRequirementsRegex = new Regex("^((?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*^[a-zA-Z0-9]).{8,})", RegexOptions.Compiled);

    public static void Main()

    {

        Console.WriteLine(PasswordRequirementsRegex.IsMatch("Password"));       

        Console.WriteLine(PasswordRequirementsRegex.IsMatch("P1234_"));

        Console.WriteLine(PasswordRequirementsRegex.IsMatch("Password1234!"));

        Console.WriteLine(PasswordRequirementsRegex.IsMatch("Password1234@!"));

    }

}