static void Main(string[] args)
{
var ym1 = new YearMonth(2019, 2);
var ym2 = new YearMonth(2017, 12);
var ym3 = new YearMonth(2016, 2);
var ym4 = new YearMonth(2013, 11);
var ym5 = new YearMonth(2019, 12);
var ym = new YearMonth[] { ym1, ym2, ym3, ym4, ym5 };
for (int i = 0; i < ym.Length; i++)
{
Console.WriteLine(ym[i]);
}
string a = ym.Contains(Is21(ym)) ? Is21(ym).Year.ToString(): "21世紀のデータがありません";
Console.WriteLine(a);
var years = ym.Select(s => s.AddOneMonth()).OrderBy(y => y.Year);
foreach (var b in years)
{
Console.WriteLine(b);
}
}