I need Java help (very simple code)

[Crossbourne]

Just started learning some Java in this online course created by the University of Helsinki. There's a small exercise I'm having trouble with. 

 

And here's a link to my code - https://pastebin.com/W0MACx1i

Here's a screenshot of the exercise. I'll appreciate any kind of help!

 

The problem: when I enter 2012 for example, it says it isn't a leap year, even though it is!

[minibois]

The issue with your code is the else if, which checks if the number is divisble by 100 and 400.

During this check, most numbers will fall there.

 

What you're checking if a number is BOTH not divisble by 100 and not divisble by 400. Most number are not cleanly divisble by those two, thus it will trigger as 'not a leap year'.

 

Something like this would work:

if(myYear % 4 == 0)
{
	if(myYear % 400 == 0 || myYear % 100 != 0)
	{
		System.out.println("The year is a leap year.");
	}
	else
	{
		System.out.println("The year is not a leap year.");
	}
}
else
{
	System.out.println("The year is not a leap year.");
}

 It isn't the cleanest code, but I felt it was a bit clearer than then neater variant (which I paste below in the spoiler).

It first checks if a number is divisible by 4. This is the first requirement, easy enough.

Then, follow another if with a OR (||) comparison. If either one or both of the comparisons returns true, it's a match.

 

What it's checking there is:

- is the number cleanly divisible by 400? Then it will be a leap year, no need to even go over the second comparison.

- The second comparison, is the number NOT divisible by 100? With these two checks, I will make sure every "divisible by 100" number will fall away, while all divisible by 4 AND 400 numbers will succeed.

 

The ugliness in that code would be the two else + System.out.println statements.

By combining the two ifs, you get this cleaner code:

Spoiler

if((myYear % 4 == 0) && (myYear % 100 != 0 || myYear % 400 == 0))
{
	System.out.println("The year is a leap year.");
}
else
{
	System.out.println("The year is not a leap year.");
}

Here I do the same as the above code, except in one single if-statement. So first check if it's divisible by 4, then (separated by parenthesis) it checks the 100/400 stuff.

Result of either code:

 

If anything was unclear, be sure to press the quote button and I would be happy to help you further!

[AbydosOne]

20 minutes ago, Crossbourne said:

Just started learning some Java in this online course created by the University of Helsinki. There's a small exercise I'm having trouble with. 

 

And here's a link to my code - https://pastebin.com/W0MACx1i

Here's a screenshot of the exercise. I'll appreciate any kind of help!

 

The problem: when I enter 2012 for example, it says it isn't a leap year, even though it is!

My work was sniped my @minibois. Their work seems to cover everything. A few notes, though...

 

I believe Integer.parseInt is preferred to Integer.valueOf; alternatively, you could use Scanner.nextInt and skip that step entirely.

 

Also, don't forget to close your Scanner (scan.close()) at the end of your program, as good Java etiquette.

[Crossbourne]

@minibois @AbydosOne Thank you so much to both of you guys! I was initially confused about the criteria regarding the calculation of leap years. Turns out it should be divisible by all three numbers (4, 100, 400). I was also worried about nested if else statements, but you just taught me a better way to do it. Much appreciated!

[Crossbourne]

This is what really confused me at first. 

[minibois]

11 hours ago, Crossbourne said:

@minibois @AbydosOne Thank you so much to both of you guys! I was initially confused about the criteria regarding the calculation of leap years. Turns out it should be divisible by all three numbers (4, 100, 400). I was also worried about nested if else statements, but you just taught me a better way to do it. Much appreciated!

The way leap years work, you just have look at a year and check these two criteria:

- divisible by 4 and NOT by 100? Leap year.

- divisible by 400? Leap year.

Anything else isn't a leap year, so it's all about writing something that checks both these scenarios.

11 hours ago, Crossbourne said:

This is what really confused me at first. 

It has always been a debate whether you should start from a place where you know it's true or false.

Personally I have always learned: assume the number will fail (won't be a leapyear) unless proven otherwise (by and if statement).

So by that logic, I would do an if statement to see if a number falls within the requirements and otherwise it will fall into else statement and won't work.

 

EDIT: I just realized this comparison is way simpler and cleaner:

if(((myYear % 4 == 0) && (myYear % 100 != 0)) || (myYear % 400 == 0))
{
	console.log("The year is a leap year.");
}
else
{
	console.log("The year is not a leap year.");
}

This just checks these two:

Quote

- divisible by 4 AND not by 100?

OR

- divisible by 400?

= true