How to loop through an array in php

PHP is a widely used programming language that is easy to use, open and efficient. In PHP, arrays are a very important data structure, and looping through arrays is also one of the basic operations in daily development. In this article, we will explore how to loop through an array in PHP.

Arrays in PHP

In PHP, an array is a collection used to store the same type of data. Arrays can store various types of data, including integers, floating point numbers, strings, Boolean values, etc. In PHP, arrays can be declared in the following ways:

//使用array()函数声明数组
$arr = array(1,2,3);

//使用[]操作符声明数组
$arr = [1,2,3];

There are three types of arrays in PHP: indexed arrays, associative arrays, and multidimensional arrays.

1. Index array

Index array is the most commonly used array type. It is an array type that uses numeric indexing to access array elements. In PHP, you can declare an indexed array in the following way:

//使用array()函数声明索引数组
$arr = array(1,2,3);

//使用[]操作符声明索引数组
$arr = [1,2,3];

2. Associative array

Associative array is an array type that uses key-value pairs to access array elements. In PHP, you can declare an associative array in the following way:

//使用array()函数声明关联数组
$arr = array("name"=>"Tom", "age"=>18);

//使用[]操作符声明关联数组
$arr = ["name"=>"Tom", "age"=>18];

The keys and values ​​in an associative array can be any type of data, and the keys must be unique. Elements in an associative array can be accessed using keys as follows:

echo $arr["name"]; //输出Tom
echo $arr["age"]; //输出18

3. Multidimensional Array

A multidimensional array is an array type that contains one or more arrays. In PHP, multidimensional arrays can be declared using:

//使用array()函数声明多维数组
$arr = array(
    array(1,2,3),
    array(4,5,6),
    array(7,8,9)
);

//使用[]操作符声明多维数组
$arr = [
    [1,2,3],
    [4,5,6],
    [7,8,9]
];

In a multidimensional array, each array can be an array of any type or an array of the same type.

Looping through arrays in PHP

In PHP, looping through arrays is a common operation. Looping through an array allows us to easily obtain each element in the array and process it.

The following are several commonly used ways to loop through arrays in PHP:

1. Use a for loop to traverse the index array

If the array is an index array, you can use The for loop iterates through the array. The for loop needs to specify the number of loops to traverse the array, and the loop variable can obtain the array elements by index. The code is as follows:

$arr = array(1,2,3,4,5);
$len = count($arr);
for ($i=0; $i<$len; $i++) {
    echo $arr[$i];
}

2. Use foreach loop to traverse index arrays and associative arrays

If the array is an index array or associative array, then you can use foreach loop to traverse the array, this is in PHP One of the most commonly used ways to traverse an array. The foreach loop can automatically obtain array elements without specifying the number of loops, which is very convenient. The code is as follows:

//遍历索引数组
$arr = array(1,2,3,4,5);
foreach ($arr as $value) {
    echo $value;
}

//遍历关联数组
$arr = array("name"=>"Tom", "age"=>18);
foreach ($arr as $key=>$value) {
    echo $key.":".$value;
}

3. Use a while loop to traverse the index array

Using a while loop to traverse an array requires obtaining the array length in advance, and then using the loop variable as an index to obtain the array elements. The code is as follows:

$arr = array(1,2,3,4,5);
$len = count($arr);
$i = 0;
while ($i < $len) {
    echo $arr[$i];
    $i++;
}

4. Use do-while loop to traverse the index array

Using do-while loop to traverse the array is similar to using while loop, except that the loop body is executed first and then the condition is checked. The code is as follows:

$arr = array(1,2,3,4,5);
$len = count($arr);
$i = 0;
do {
    echo $arr[$i];
    $i++;
} while ($i < $len);

5. Use the list() function to traverse the associative array

Using the list() function can easily assign the value of the associative array to a variable. The code is as follows:

$arr = array("name"=>"Tom", "age"=>18);
list($name, $age) = $arr;
echo $name;
echo $age;

Summary

This article introduces the concept of arrays in PHP and how to use for loops, foreach loops, while loops, do-while loops and list() functions to traverse arrays. Depending on the type of array, different looping methods can be selected. Proficient in the skill of looping through arrays can greatly improve the efficiency of the program and speed up development.

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