PHP Learning (11)--Arrays and Data Structures PHP Learning Videos PHP Learning Materials PHP Learning Tutorials

Arrays and data structures in PHP

Arrays are one of the most important data types in the PHP language and are widely used in PHP. Because PHP is a programming language with weak data types, array variables in PHP can store any number of data of any type, and can realize the functions of data structures such as heaps, stacks, and queues in other strong data types. The purpose of using an array is to organize multiple interrelated data together to form a set and use it as a unit to achieve the purpose of batch data processing.

Classification of arrays

The essence of an array is to store, manage and operate a set of variables. Arrays are also one of the 8 data types provided by PHP and are composite data types.

A single value stored in an array is called an element of the array. Each array element has an associated index, which can be regarded as the identifying name of the data content in this array, often called an array subscript. You can use the subscript in the array to access the element corresponding to the subscript, or you can call the subscript a key name. The association between the key and the value is usually called a binding, and the keys and values ​​map to each other. In PHP, arrays are divided into indexed arrays (indexed) and associative arrays (assocative) based on the different ways in which arrays provide subscripts. The index value of the index array is an integer. Starting with 0 and increasing in sequence. Associative arrays use strings as index values.

Definition of array

PHP does not need to specify the size of the array when creating it, or even declare it before using it, and can store any type of data in the same array. PHP supports one-dimensional and multi-dimensional arrays, which can be created by users, or arrays can be generated from database queries by some specific database processing functions, and some other functions return arrays. There are two methods for customizing arrays in PHP: directly Arrays can be declared by assigning values ​​to array elements; arrays can be declared using the array() function.

1. Declare the array by direct assignment

$array variable name [subscript] = data content

(1) Since there is no size limit for arrays in PHP, they should be paired together when initializing the array. The array is declared.

(2) Sometimes when debugging a program, if you just want to see the subscripts and values ​​of all elements in the array in the program, you can use the print_r() or var_dump() function to print the contents of all elements in the array.

(3) When declaring an index array, if the index value is increasing, you do not need to specify the index value in square brackets. The default index value starts from 0 and increases in sequence.

(4) In PHP, the subscripts of the index array can be non-continuous values, as long as the non-continuous subscript values ​​are specified during initialization. If the specified subscript value has been declared, it is a reassignment of the variable. If elements without a specified index value are assigned together with elements with a specified index value, the default index value of the element without a specified index value will be incremented by the highest index value among the elements with a specified index value.

2. Use the array() language structure to create a new array

$Array variable name = array(key1 => value1, key2 => value2 ,..., keyN => valueN);

If not applicable The "=>" symbol specifies the subscript, which defaults to an index array.

3. Declaration of multi-dimensional array

An array is a named area used to store a series of variable values. In PHP, arrays can store all types of data supported in PHP, including storing array type data in arrays. If the elements in the array are still arrays, they constitute an array containing arrays, that is, a multidimensional array.

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