How to determine the leap year?

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How to determine the leap year?

by Puthyrak Kang
June 28, 2009

A leap year (or intercalary year) is a year containing one or more extra days (or, in the case of lunisolar calendars, an extra month) in order to keep the calendar year synchronized with the astronomical or seasonal year. February in a leap year has 29 days instead of the usual 28 so the year lasts 366 days instead of the usual 365.

Algorithm

if year modulo 400 is 0 then leap
else if year modulo 100 is 0 then  no_leap
else if year modulo 4 is 0 then leap
else no_leap

Code

<script text="text/javascript">
function isLeap(year){
  if(year % 400 == 0){
     return true;
  }
  if(year % 100 == 0){
     return false;
  }
  if(year % 4 == 0){
     return true;
  }
  return false;
}
</script>

References

(1) Aland Shalloway & James R. Trott, Design Patterns Explained, Second Edition.

(2) Allen Holub, Holub on Patterns, Learning Design Patterns by Looking at Code

(3) Eric Evans, Domain-Driven Design, Tackling complexity in the heart of software.