Persons

using System;
using System.Text.RegularExpressions;

class Persons
{
    class Person
    {
        private string name;
        private int age;
        private string email;

        public string Name
        {
            get
            {
                return this.name;
            }
            set
            {
                if (String.IsNullOrWhiteSpace(value))
                {
                    throw new ArgumentException("Name cannot be empty.");
                }

                if (!ValidateName(value))
                {
                    throw new ArgumentException("Name should contain only Latin letters, spaces and hyphens and start with an uppercase letter.");
                }

                this.name = value;
            }
        }

        public int Age
        {
            get
            {
                return this.age;
            }
            set
            {
                if (!ValidateAge(value))
                {
                    throw new ArgumentOutOfRangeException("Age should be an integer between 1 and 100 inclusive.");
                }

                this.age = value;
            }
        }

        public string Email
        {
            get
            {
                return this.email;
            }
            set
            {
                if (String.IsNullOrWhiteSpace(value))
                {
                    throw new ArgumentException("Email cannot be empty.");
                }

                if (!ValidateEmail(value))
                {
                    throw new ArgumentException("Email could not be validated."); // Put a more descriptive message
                }

                this.email = value;
            }
        }

        private bool ValidateName(string name)
        {
            Regex nameMatcher = new Regex(@"^[A-Z][a-zA-Z- ]+$");
            return nameMatcher.IsMatch(name);
        }

        private bool ValidateAge(int age)
        {
            if (age < 1 || age > 100)
            {
                return false;
            }
            return true;
        }

        private bool ValidateEmail(string email)
        {
            // For info on the regex check out http://www.regular-expressions.info/email.html
            Regex emailMatcher = new Regex(@"^[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$");
            return emailMatcher.IsMatch(email);
        }

        public Person(string name, int age)
        {
            this.Name = name;
            this.Age = age;
        }

        public Person(string name, int age, string email)
        {
            this.Name = name;
            this.Age = age;
            this.Email = email;
        }

        public override string ToString()
        {
            return "This is a person called " + this.name + ". He/she is " + this.age + " years old. His/her email address is " + (string.IsNullOrEmpty(this.email) ? "not set." : this.email);
        }

        public void IntroducePerson()
        {
            Console.WriteLine("Hi, my name is {0} and I'm {1} years old.", this.name, this.age);
        }
    }

    static void Main()
    {
        Person gosho = new Person("Gosho", 29); // using first constructor
        Person pesho = new Person("Pesho", 33, "pesho@mail.bg"); // using second constructor

        Console.WriteLine(gosho); // print a person using the overridden ToString() method for the Person class
        Console.WriteLine(pesho);
        Console.WriteLine(pesho.Name);
        pesho.IntroducePerson(); // use a non-static method from the Person class

        // Person withBadName = new Person("few", 12); // throws exception because name is not valid
        // Person withBadAge = new Person("Hey", "not age"); // compile-time error - no overload for the Person constructor takes two strings; age is mandatory
        // Person withOutOfRangeAge = new Person("Hello", 122); // throws ArgumentOutOfRangeException because age is not in the accepted interval [1 ... 100]
        // Person withBadEmail = new Person("Hey", 100, "asdf"); // throws exception because email is not valid
        // Person withEmptyName = new Person("", 22); // throws exception because name is empty
        // Person withEmptyEmail = new Person("Baba Ilyitsa", 1, ""); // throws exception because email is empty
    }
}