Math problem in java trying to figure out whats wrong with my code

Question

so the code works but some years which should be leap years are not like 2008 is showing its not a leap year which it was.

//is leap year if...
      if ((whichYear % 4 == 0) && (whichYear % 100 == 0) && (whichYear % 400 == 0))      
         {
          isLeapYear = true;
          daysLeftInYear = 366;                          
          System.out.println("true " + daysLeftInYear);
         } 

         else 
              {
               isLeapYear = false;
               daysLeftInYear = 365;
               System.out.println("false " + daysLeftInYear);
              }

Your current logic says that a leap year must be divisible by 4 AND 100 AND 400. That's probably not what you meant. — assylias, Feb 04 '20 at 14:17
A number that is devisable by 100 is surely also devisable by 4, isn´t it? So your first check is equivalent to just `if(whichYear % 400 == 0)`. Thus your entrie defintion of a leapyear is "every year that is divable by 400". — MakePeaceGreatAgain, Feb 04 '20 at 14:18
my teacher wants the program to go through these steps // 1. If the year is evenly divisible by 4, go to step 2. Otherwise, go to step 5. // 2. If the year is evenly divisible by 100, go to step 3. Otherwise, go to step 4. // 3. If the year is evenly divisible by 400, go to step 4. Otherwise, go to step 5. // 4. The year is a leap year (it has 366 days). // 5. The year is not a leap year (it has 365 days). — data10019, Feb 04 '20 at 14:18
Leap Years are years which are divisible by 4.Except for century years which must be divisible by 400. Your logic used in the ' if ' condition is wrong. — Navidk, Feb 04 '20 at 14:18
think i figured it out : is a leap year if it can be evenly divided by 4; If the year can be evenly divided by 100, it is NOT a leap year, unless; The year is also evenly divisible by 400. Then it is a leap year. — data10019, Feb 04 '20 at 14:22
While you can do this with a one line expression, you may find it easier to write some if/else statements that exactly mimic what your teacher asked for. You can even put comments like `// Step 3` in your code. It may look longer, but it won’t be any slower than the one-line version. — VGR, Feb 04 '20 at 15:32

score 0 · Answer 1 · answered Feb 04 '20 at 14:23

0

The easiest way is to just break it down into two possibilities.

If (year % 100 == 0) {
  // if century year
} else {
  // if not century year.
}

The rest is up to you.

answered Feb 04 '20 at 14:23

WJS

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score 0 · Answer 2 · answered Feb 04 '20 at 14:25

Well of course it won't work with 2008 :) Because you defined leap years as being divisible by 4 AND divisible by 100 AND divisible by 400 :) With this definition only every 400th year will be a leap year, for example 1600.

The correct definition of a leap year is: Divisible by 4 AND if it is divisible by 100, then also divisible by 400. For example 1700 is not a leap year, but 1200 is.

So in terms of Java this would lead to:

int year; // initialize it with some year
boolean leapYear = year % 4 == 0 && ((year % 100 == 0) == (year % 400 == 0))

Math problem in java trying to figure out whats wrong with my code

2 Answers2