基準となる日から今日までの経過年数を算出する

Dim dtmToday As DateTime = DateTime.Now
Dim dtmSomeday As New DateTime(1987, 5, 7)

Dim intYearsPassage As Integer = dtmToday.Year - dtmSomeday.Year

Dim dtmSamedayInThisYear As New DateTime(dtmToday.Year, dtmSomeday.Month, dtmSomeday.Day)

If dtmSamedayInThisYear > dtmToday Then intYearsPassage -= 1

Console.WriteLine("今日: " + dtmToday.ToShortDateString())
Console.WriteLine("基準となる日: " + dtmSomeday.ToShortDateString())
Console.WriteLine("経過年数: " + intYearsPassage.ToString())

DateTime dtmToday   = DateTime.Now;
DateTime dtmSomeday = new DateTime( 1987, 5, 7 );

int iYearsPassage = dtmToday.Year - dtmSomeday.Year;

DateTime dtmSamedayInThisYear = new DateTime( dtmToday.Year, dtmSomeday.Month, dtmSomeday.Day );

if ( dtmSamedayInThisYear > dtmToday ) iYearsPassage -= 1;

Console.WriteLine( "今日: " + dtmToday.ToShortDateString() );
Console.WriteLine( "基準となる日: " + dtmSomeday.ToShortDateString() );
Console.WriteLine( "経過年数: " + iYearsPassage.ToString() );