How to modify the array in php foreach loop

PHP is a powerful programming language that provides many convenient and easy-to-use array processing functions, of which foreach loop is one of them.

In PHP, foreach Loops can be used to iterate through all elements in an array and operate on them. If you want to modify the elements in the array, foreach loop is a more convenient method. The following will introduce how the foreach loop modifies the array.

Basic syntax

foreachThe basic syntax of the loop is as follows:

foreach($array as $key => $value){
  // 对元素进行操作
}

Among them, $array represents the array to be traversed, $key represents the key of the current element, $value represents the value of the current element. foreachThe loop will traverse all the elements in the array and perform the operation in the loop body once for each element.

Modify array elements

To modify the array elements, just operate on the elements in the loop body. For example, suppose there is an associative array $arr whose elements are 'name' => 'Tom', 'age' => 20, 'gender' => 'male', we want to change the value of the 'age' element to 25, we can use the foreach loop to achieve this:

$arr = ['name' => 'Tom', 'age' => 20, 'gender' => 'male'];
foreach($arr as $key => $value){
  if($key == 'age'){
    $arr[$key] = 25;
  }
}
print_r($arr);

The output result is Array ([name] => Tom [age] => 25 [gender] => male ). It can be seen that the foreach loop can easily modify the elements in the array.

Modify all elements

If you want to modify all elements, just operate on $value in the loop body. For example, suppose there is an index array $arr whose elements are [1, 2, 3, 4, 5], and we want to multiply the values ​​of all elements in it by 2, You can use a foreach loop to achieve this:

$arr = [1, 2, 3, 4, 5];
foreach($arr as $key => $value){
  $arr[$key] = $value * 2;
}
print_r($arr);

The output result is Array ( [0] => 2 [1] => 4 [2] => 6 [ 3] => 8 [4] => 10 ). As you can see, the foreach loop easily completes the modification of all elements in the array.

Modify some elements

If you only want to modify some elements in the array, you can use the if statement to determine the elements to be modified. For example, suppose there is an associative array $arr whose elements are 'name' => 'Tom', 'age' => 20, 'gender' => 'male', we want to change the value of the 'age' element to 25, and only modify the 'age' element. We can use the if statement to achieve this:

$arr = ['name' => 'Tom', 'age' => 20, 'gender' => 'male'];
foreach($arr as $key => $value){
  if($key == 'age'){
    $arr[$key] = 25;
  }
}
print_r($arr);

The output result is Array ( [name] => Tom [age] => 25 [gender] => male ). It can be seen that the foreach loop uses the if statement to determine the elements to be modified, and realizes the modification of some elements.

Notes

When using foreach to modify the array in a loop, you need to pay attention to the following points:

1. Must be passed by reference, otherwise it will be modified The value will not take effect.

For example, suppose there is an associative array $arr whose elements are 'name' => 'Tom', 'age' => 20, ' gender' => 'male', if you use the following code to modify the value of the 'age' element, it will not actually take effect:

foreach($arr as $key => $value){
  if($key == 'age'){
    $value = 25;
  }
}

because $value is a copied value, modifying it will not affect the original array. If you want to modify the original array, you must use reference transfer, that is, add the & symbol before the loop variable:

foreach($arr as $key => &$value){
  if($key == 'age'){
    $value = 25;
  }
}

At this time, modifying the value of $value will take effect , and will affect the original array.

2. It is not recommended to add or remove array elements in a loop, which may lead to unexpected results and errors. If you need to add or remove elements, it is recommended to do so after the loop has completed.

Summary

foreachLooping is a convenient way to traverse an array and can also be used to modify elements in an array. To modify an array element, just operate on the corresponding element in the loop body. If you want to modify all elements, you only need to operate $value; if you only need to modify some elements, you can use the if statement to judge.

When using foreach to modify an array in a loop, you need to pay attention to reference passing and it is not recommended to add or delete elements in the loop. Mastering the skills of using foreach loops can make it easier to process arrays.

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