How To Generate The Last Date Of Every Month Of A Year With LINQ In C# & .NET

I recently need to generate the last day of each month, for some processing in an algorithm.

The default goto would be this:

public IEnumerable<DateOnly> GetDatesInYear(int year)
{
  var temp = new DateOnly(year, 1, 1);
  while (temp.Year == year)
  {
    yield return temp.AddMonths(1).AddDays(-1);
    temp = temp.AddMonths(1);
  }
}

Straightforward enough.

You can also achieve the same thing using a LINQ expression.

public IEnumerable<DateOnly> GetDatesInYear(int year)
{
	return Enumerable.Range(1, 12).Select(x => new DateOnly(year, x, DateTime.DaysInMonth(year, x)));
}

This can be visualized with this harness:

var year = 2026;
foreach (var date in GetDatesInYear(year))
{
	Console.WriteLine(date);
}

The code is in my GitHub.

Happy hacking!