含糊不清的三元陈述

Question

Working on a simple project, the objective is to find whether or not it is a leap year. In PHP, I attempted to use a ternary rather then the standard elseif statements.

$year = 2000;
$is_leapYear = ($year%400 == 0)? true: ($year%100 == 0)? false: ($year % 4 == 0);
echo ($year % 400 == 0) .'.'. ($year % 100 == 0) .'.'. ($year % 4 ==0);
echo $year . ' is ' . ($is_leapYear ? '' : 'not') . ' a leap year';

I discovered that this doesn't work because of a lack of parenthesis. Here is the correct solution:

$is_leapYear = ($year % 400 == 0)? true: (($year % 100 == 0)? false: ($year%4 == 0));

My question is why do ternary operators need parenthesis on the top true or false branch? I don't think the above code is ambiguous.

Answer 1

There's no need for such complicated code. PHP's date() can return whether it's a leap year or not:

$is_leap_year = (bool) date('L', mktime(0, 0, 0, 1, 1, $year));

See manual here.