using System.Text.RegularExpressions;  // Regex

Write("Enter your age: ");
string input = ReadLine()!; // null-forgiving

Regex ageChecker = new(@"^\d+$");

if (ageChecker.IsMatch(input))
{
  WriteLine("Thank you!");
}
else
{
  WriteLine($"This is not a valid age: {input}");
}

string films = "\"Monsters, Inc.\",\"I, Tonya\",\"Lock, Stock and Two Smoking Barrels\"";

WriteLine($"Films to split: {films}");

string[] filmsDumb = films.Split(',');

WriteLine("Splitting with string.Split method:");
foreach (string film in filmsDumb)
{
  WriteLine(film);
}

Regex csv = new(
  "(?:^|,)(?=[^\"]|(\")?)\"?((?(1)[^\"]*|[^,\"]*))\"?(?=,|$)");

MatchCollection filmsSmart = csv.Matches(films);

WriteLine("Splitting with regular expression:");
foreach (Match film in filmsSmart)
{
  WriteLine(film.Groups[2].Value);
}