In PHP, judging leap years can be achieved through the date() function or manual logic. 1. The leap year rules are: it can be divisible by 4 but cannot be divisible by 100, or it can be divisible by 400; 2. Use date('L') to directly return the Boolean value, the advantage is that the code is simple but depends on the system date mechanism; 3. Manual implementation checks whether it can be divisible by 4, 100, and 400 through the order of judgment, with clear structure and easy to test; 4. In actual applications, the method is selected according to the needs, and the date() is recommended for simple scenarios, and when you need to control logic, you can use custom judgment. Both methods are effective, depending on the specific project requirements.

It is actually not difficult in PHP to determine whether a year is a leap year. The key is to understand the rules of leap year and implement it correctly with code. PHP itself does not have a special built-in function to directly judge leap years, but we can do it with the help of date() or manual logic.

1. What is a leap year?

Before starting to write code, let’s clarify the criteria for judging leap years :

• A leap year that can be divided by 4 but cannot be divided by 100;
• Or it is also a leap year that can be divided by 400.

for example:

• 2000 is a leap year (it can be divisible by 400);
• 1900 is not a leap year (it can be divided by 100 but cannot be divided by 400);
• 2024 is a leap year (can be divisible by 4 and not divisible by 100).

2. Use the date function to judge leap years

PHP provides an easy way: use date('L') to determine whether a year is a leap year. This formatted character returns a Boolean value.

 function isLeapYear($year) {
    return (bool) date('L', strtotime("$year-01-01"));
}

Call method:

 var_dump(isLeapYear(2024)); // true
var_dump(isLeapYear(1900)); // false

? Advantages : The code is concise and you don’t need to deal with the judgment logic yourself;
??Note : Relying on the system's date processing mechanism, if your application requires very high accuracy or cross-platform compatibility, manual judgment may be considered.

3. Manually implement leap year judgment logic

If you don't want to rely on date() function, you can also manually write logical judgments based on the definition of leap years:

 function isLeapYear($year) {
    if ($year % 4 != 0) {
        return false;
    } elseif ($year % 100 != 0) {
        return true;
    } else {
        return ($year % 400 == 0);
    }
}

The structure of this code clearly reflects the order of judgment of leap years:

• Let’s see if it can be divided by 4;
• If it can be divided by 100, it must be seen if it can be divided by 400;
• Otherwise it will be a leap year.

This method is more intuitive and easier to test and debug.

4. Suggestions for actual use scenarios

In actual projects, you may encounter these situations:

• The form has submitted a year to verify that it is a leap year;
• You need to know how many days February will be when generating your calendar;
• The leap year impact is considered when calculating the number of days in a certain date range.

At this time, you can choose one of the above two methods according to the specific situation. If you make a simple judgment, it is recommended to use date('L') ; if higher control or testability is required, the logic is implemented manually.

Basically that's it. Both methods can effectively judge leap years, and which one to choose depends on your specific needs and coding style.

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