Let's talk about the specific way of writing array subscripts in PHP

The subscript of an array in PHP can be indexed using integer, string and Boolean types, and you can even use one array as the subscript of another array. The following will introduce the specific writing methods of array subscripts in PHP.

1. Integer subscript

The integer subscript in the PHP array is the same as the ordinary array subscript, starting from 0 and gradually increasing. For example, an array with 5 elements starting from 0 can be written as:

$arr = array(1, 2, 3, 4, 5);

The subscripts in this array are 0, 1, 2, 3, and 4 respectively. If you need to add elements to the end of the array, you can use the following code:

$arr[] = 6;

After executing the above code, the array will append an element with a value of 6 at the end and set its subscript to 5.

2. String subscript

PHP array string subscript allows developers to use strings as array subscripts. For example:

$arr = array(
    "name" => "Tom",
    "age" => 20,
    "gender" => "male"
);

In the above example, each element in the array has a string enclosed in quotes as a subscript. For this type of subscript, there are two ways to access the elements in the array.

The first is to directly use the subscript string to access:

echo $arr["name"];

The above code will output "Tom".

The second is to use curly braces {} to wrap the subscript string:

echo $arr{"name"};

The above code also outputs "Tom".

3. Boolean subscript

The Boolean subscript in PHP only allows the use of two values: true and false. If you use another value as an array subscript, PHP will automatically convert it to a Boolean type. Therefore, usually only the values ​​true and false are legal subscripts.

For example:

$arr = array(
    true => "Hello",
    false => "World"
);

In the above example, the value of the element with index true is "Hello", and the value of the element with index false is "World".

4. Array as subscript

The array subscript in PHP can also be another array. For example:

$arr1 = array('a', 'b', 'c');
$arr2 = array($arr1, 'd', 'e');

In the above example, the first element in the $arr2 array is the $arr1 array, so it can be accessed using:

echo $arr2[0][1];

The output result is "b".

Summary

The above are several ways to write array subscripts in PHP. No matter which subscript is used, it should be used reasonably to improve the maintainability and complexity of PHP applications.

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