There are several indexes for php array types

PHP is a programming language widely used in web development. In PHP, an array is a frequently used data type used to store a series of similar types of data. In an array, you can use an index to access each element in the array. An index is a number or string that identifies the position of an element in an array. In PHP, there are two index types for array types: numeric index and associative index.

Numeric index

Numeric index is the most common type of array index. The elements in an array are ordered according to their position in the array and are assigned a numeric index. Numeric indexing starts at 0 and increases by 1 for each element. Array elements can be referenced using subscripts and braces.

The following is an example of a PHP array containing numeric indexes:

$students = array("Tom", "Jerry", "Mickey", "Donald");

//访问数组元素
echo $students[0]; //输出Tom
echo $students[1]; //输出Jerry

In the above code, we define an array named $students and use four strings as array elements . We can access each element in the array using numeric index 0, 1, 2, 3.

Associative Index

Associative index is a more flexible type of index that uses string keys to identify array elements instead of numeric indexes. Each array element consists of a key-value pair, where the key is a string and the value can be any type of data. In associative arrays, key-value pairs must be separated by the => symbol.

The following is an example of a PHP array containing an associative index:

$student_grades = array("Tom" => 85, "Jerry" => 92, "Mickey" => 78, "Donald" => 89);

//访问数组元素
echo $student_grades["Tom"]; //输出85
echo $student_grades["Jerry"]; //输出92

In this example, we define an associative array named $student_grades, where each key name is a student The name, each key value represents the score of the student. We can use each student's name as a key to access their grades.

In addition to numeric indexes and associative indexes, two new index types are introduced in PHP 7.4: object index and empty index. Object indexing allows using an object as an array index, while null indexing allows using an empty position as an array index.

Summary

In PHP, there are two common index types for array types: numeric index and associative index. Numeric indexing is the most common and basic type of array indexing, which uses numbers to identify each element position in an array. Associative indexes are a more flexible and adaptable type of index that use strings to identify array elements, with each element consisting of a key-value pair. In addition to this, two new index types were introduced in PHP 7.4: object index and null index. Understanding the different index types helps us better understand array operations in PHP and provides support for implementing more efficient code.

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