Traversing array methods in php_PHP tutorial

There are many ways to implement array traversal:

1. Continuously indexed array:

It is very simple to implement continuous array traversal, because the index of the array is continuous (0 1 2...), so we can first use the count() function to calculate the number of elements in the array, and then create a for loop, As follows:

$subject=array("maths","english","physics");

　$num_elements=count($subject); //The value of $num_elements is 3

　for ($i=0;$i<$num_elements; ++$i){

echo ("$subject[$i]

　n");

　}

The result is:

Maths

English

physics

Here we assign an initial value of 0 to $i because the index of the array element is 0 1 2 by default. If the index of the first element is not 0, we only need:

$subject=array(3=>"maths","english","physics");

　$num_elements=count($subject)+3; //Pay attention here

　for ($i=3;$i<$num_elements; ++$i){

echo ("$subject[$i]

　n");

　}

Here $i is assigned a value of 3, and $num_elements=count($subject)+3. This is easily overlooked.

2. Array of non-consecutive indexes:

$subject=array("m"=>"maths","e"=>"english","p"=>"physics");

An array is created here with the index values ​​"m" "e " "p" respectively. How to traverse such an array?

Method 1: Use list() and each() function combination

$subject=array("m"=>"maths","e"=>"english","p"=>"physics");

reset($subject); //Reset the pointer to the first element

While (list($key,$value)=each($subject)){

echo "$key is $value

　n"; }

Method 2: Use foreach statement

$subject=array("m"=>"maths","e"=>"english","p"=>"physics");

foreach($subject as $key => $value){

echo "$key is $value

　n";

　}

　?>

Isn’t it simpler than list() and each()?

The difference between foreach and list() each() combination:

Foreach performs operations on a copy of the original array. Its advantage is that it will not affect the position of the current array pointer. Its disadvantage is that for a large array, copying takes a long time.

List() each() combination It is obvious that after traversing and using it, the position of the pointer changes.

Method 3: Use the array_walk() function to traverse the array

Array_walk() allows users to customize functions to process each element in the array.

$subject=array("maths","english","physics");

Function printElement($element){

print ("$element

　n");

　}

array_walk($subject,"printElement");

The above is the method of traversing arrays in PHP introduced to you by Bangkejia.com. I hope it will be helpful to you.