There are two different forms of arrays in PHP

In PHP, arrays are often used as an important data structure. In PHP, arrays come in two different forms: ordinary arrays and associative arrays. The main difference between the two is how array elements are accessed and how arrays are defined.

1. Ordinary array

Ordinary array is also called index array, which is the most basic array form in PHP. Each element in a normal array has a unique numeric index, which is used to access and operate on that specific element. This index starts at 0 and is assigned to each element in the array in sequence.

Ordinary arrays are defined as follows:

$array = array('apple', 'banana', 'orange');

In this example, the array $array contains three elements, namely 'apple', 'banana' and 'orange'. The indices of these three elements are 0, 1, and 2 respectively, and these elements can be accessed through array subscripts.

The following is a practical example:

$array = array('apple', 'banana', 'orange');
echo $array[0]; // 输出‘apple’
echo $array[2]; // 输出‘orange’

Characteristics of ordinary arrays:

1. The array elements are arranged in order according to the index starting from 0;
2. The index must be an integer type;
3. If no index is used when defining the array, PHP will automatically assign indexes to them, starting from 0 and increasing;
4. If a non-numeric index is used, PHP will Cast to integer;
5. The elements in the array can be of any data type.

2. Associative array

Associative array, also called string array, is another commonly used array form. Unlike ordinary arrays, each element in an associative array has a unique string index that is used to access and operate on a specific element. This string index can be any string and can be defined according to requirements.

Associative arrays are defined as follows:

$array = array('a' => 'apple', 'b' => 'banana', 'o' => 'orange');

In this example, the array $array contains three elements, namely 'apple', 'banana' and 'orange'. The indices of these three elements are 'a', 'b' and 'o' respectively, and these elements can be accessed through these string indices.

The following is a practical example:

$array = array('a' => 'apple', 'b' => 'banana', 'o' => 'orange');
echo $array['a']; // 输出‘apple’
echo $array['o']; // 输出‘orange’

Characteristics of associative arrays:

1. Array elements are allocated according to string index;
2. The index can Is any string;
3. If no index is used when defining an array, PHP will automatically assign them an increasing integer index;
4. The elements in the array can be of any data type.

3. Comparison between ordinary arrays and associative arrays

Ordinary arrays and associative arrays have their own application scenarios in PHP. Ordinary arrays are suitable for the following situations:

1. Array elements have the same data type;
2. Array elements have no special meaning.

Associative arrays are suitable for the following situations:

1. Array elements have different data types;
2. Array elements have special meanings;
3. The index of the array element needs to be defined by yourself.

In short, ordinary arrays and associative arrays are commonly used array types in PHP. When using ordinary arrays or associative arrays, you need to choose the most appropriate data type according to actual needs in order to maximize the effect in different application scenarios.

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