うるう年の判別

プログラム例

LOGICAL FUNCTION LEAPYR(Y)

INTEGER Y

LEAPYR=.FALSE.

IF(MOD(Y,4).NE.0) RETURN

IF((MOD(Y,100).EQ.0).AND.(MOD(Y,400).NE.0)) RETURN

LEAPYR=.TRUE.

END

C====================================

C

C Which years are leap years?

C http://www.timeanddate.com/date/leapyear.html

C

C====================================

C

C In the Gregorian calendar, which is the calendar used by most modern

C countries, the following rules decides which years are leap years:

C

C 1. Every year divisible by 4 is a leap year.

C 2. But every year divisible by 100 is NOT a leap year

C 3. Unless the year is also divisible by 400, then it is still

C a leap year.

C

C This means that year 1800, 1900, 2100, 2200, 2300 and 2500 are **NOT**

C leap years, while year 2000 and 2400 are leap years.

C

C This actually means year 2000 is kind of special, as it is the first

C time the third rule is used in many parts of the world.

C

C In the old Julian Calendar, there was only one rule: Every year

C divisible by 4 is a leap year. This calendar was used before the

C Gregorian calendar was adopted.