How to iterate and access elements in PHP array

How to traverse and access elements in a PHP array

PHP is a widely used server-side scripting language that has powerful array capabilities. In PHP, an array is a data structure that can store multiple values, and can be an indexed array, an associative array, or a multidimensional array. This article explains how to iterate and access elements in a PHP array and provides corresponding code examples.

1. Traversal and access of index array

The index array is an array with integers starting from 0 as the key name. We can use a loop structure to traverse the index array and access each element in the array.

The sample code is as follows:

$fruits = array("apple", "banana", "cherry", "date");

// 使用 for 循环遍历索引数组
for ($i = 0; $i < count($fruits); $i++) {
    echo $fruits[$i] . " ";
}

// 输出结果：apple banana cherry date

In the above code, we use a for loop to traverse the index array $fruits. The initial value of the loop variable $i is 0 and increases by 1 each time through the loop until the value of $i is less than the length of the array. In the loop body, array elements are accessed by index and output.

In addition to using the for loop, we can also use the foreach loop to traverse the index array:

$fruits = array("apple", "banana", "cherry", "date");

// 使用 foreach 循环遍历索引数组
foreach ($fruits as $fruit) {
    echo $fruit . " ";
}

// 输出结果：apple banana cherry date

In the above code, $fruit is a temporary variable used to store the values ​​traversed each time the loop The value of the element. With the foreach loop, we don't need to manually manage the values ​​of the loop variables and can traverse the index array more concisely.

2. Traversal and access of associative arrays

Associative arrays are arrays that use custom string key names as indexes. Associative arrays are traversed and accessed slightly differently than indexed arrays.

The sample code is as follows:

$student = array("name" => "Tom", "age" => 20, "grade" => "A");

// 使用 foreach 循环遍历关联数组
foreach ($student as $key => $value) {
    echo $key . ": " . $value . "<br>";
}

// 输出结果：
// name: Tom
// age: 20
// grade: A

In the above code, we traverse the associative array $student through the foreach loop. The $key variable in the loop body stores the key name of the current element, and the $value variable stores the value of the current element. In this way, we can easily access each element in the associative array.

3. Traversal and access of multi-dimensional arrays

A multi-dimensional array is an array that contains other arrays in the array. When traversing and accessing multi-dimensional arrays, we need to use multi-level loop structures.

The sample code is as follows:

$students = array(
    array("name" => "Tom", "age" => 20, "grade" => "A"),
    array("name" => "Mike", "age" => 18, "grade" => "B"),
    array("name" => "Jane", "age" => 19, "grade" => "A")
);

// 使用嵌套的 foreach 循环遍历多维数组
foreach ($students as $student) {
    foreach ($student as $key => $value) {
        echo $key . ": " . $value . "<br>";
    }
    echo "<br>";
}

// 输出结果：
// name: Tom
// age: 20
// grade: A
//
// name: Mike
// age: 18
// grade: B
//
// name: Jane
// age: 19
// grade: A

In the above code, $students is a multi-dimensional array containing multiple associative arrays. Using nested foreach loops, we can iterate through each associative array in turn and output the key names and corresponding values.

Summary:

This article explains how to traverse and access elements in a PHP array. For indexed arrays, you can use for loops or foreach loops to implement traversal and access; for associative arrays, you can also use foreach loops; and multi-dimensional arrays require multi-level loops for traversal and access. If you are proficient in these methods, you will be more comfortable handling array operations.

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