功能的含义

Here is the function I'm not understanding:

$year = date("Y");
$leapYear = false;
if((($year%4==0) && ($year%100==0)) || ($year%400==0))
    $leapYear = true;

Does that mean that, if the (($year is divided by 4 but not divided by 100) or (the year is divided by 400)) that is a leap year?

I'm new to PHP, please anyone help me to understand the statements.

This is basically what is says in pseudo code

if(year is divisible by 4 or 100) {
  leapyear = true
} else if (year is divisible by 400) {
  //this will never be hit because it would meet the first case
  leapyear = true
}

Based on your code, your second guess is correct.

if((($year % 4==0) && ($year % 100==0)) || ($year % 400==0))

means that EITHER of these must be true to be a leap year:

1. ($year%4==0) && ($year%100==0)
2. $year%400==0

So a year is a leap year under these conditions:

• year is divisible by 4 and divisible by 100

OR

• year is divisible by 400

However, the code you posted is wrong in that it doesn't correctly define a leap year.

A year is a leap year if it is divisible by 4, except when it is divisible by 100 and not divisible by 400. So in your if statement the ($year % 100 == 0) should be ($year % 100 != 0)

So the proper logic would be this:

if ((($year % 4 == 0) && ($year % 100 != 0)) || ($year % 400 == 0))
    $leapYear = true;

Regarding the &&:

&& means AND, and the expression A && B is either true or false.

By definition, A && B is true only if both A and B are true. If any of them are false, then A && B is false.

I think you're likely confused because the code you've provided doesn't find leap years. Leap years are divisible by 4 but NOT 100.. unless they are also divisible by 400. If you flip the logic around, it's easier to look at. If it's divisible by 400, it's a leap year, no matter what. Otherwise, it's a leap year if it's divisible by 4 and NOT divisible by 100.

// pseudocode
if ( year % 400 == 0  || (year % 4 == 0 && year % 100 != 0))
    return true;
else
    return false;

You can play around with it and just say:

return year % 400 == 0  || (year % 4 == 0 && year % 100 != 0)

The && means both sides have to be true in order for && to return true.