Array walk function in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the array_walk() function do in PHP?

It applies a user-defined function to every element of an array, allowing you to modify or use each element.

beginner

How do you define the callback function used in array_walk()?

The callback function takes at least one parameter: the value of the current element, passed by reference if you want to modify it. It can also take a second optional parameter for the key.

intermediate

What is the difference between array_walk() and array_map()?

array_walk() applies a function to each element and can modify the original array by reference. array_map() returns a new array with the results and does not modify the original array.

beginner

Can array_walk() modify the original array elements?

Yes, if the callback function uses the value parameter by reference, it can change the original array elements.

beginner

Write a simple example of array_walk() that appends '!' to each string in an array.

Example:<br><pre>function addExclamation(&$item, $key) {
  $item .= '!';
}
$array = ['Hi', 'Hello', 'Hey'];
array_walk($array, 'addExclamation');
// Result: ['Hi!', 'Hello!', 'Hey!']</pre>

What parameters does the callback function for array_walk() receive?

A Value and key of each array element

B Only the value of each element

C Only the key of each element

D The entire array

The callback function receives the value and key of each element to allow processing or modification.

Does array_walk() return a new array?

A No, it returns the original array

B Yes, always

C Yes, but only if the callback returns a value

D No, it returns true or false

array_walk() returns true on success or false on failure; it does not return a new array.

How can you modify the original array elements inside the callback?

A You cannot modify original elements

B By passing the value parameter by reference

C By using a global variable

D By returning the new value from the callback

Passing the value parameter by reference (&$item) allows modifying the original array elements.

Which function is better to create a new array with modified values without changing the original array?

A array_walk()

B array_filter()

C array_map()

D array_reduce()

array_map() returns a new array with modified values, leaving the original unchanged.

What happens if the callback function in array_walk() does not accept the key parameter?

A The key is ignored and only the value is passed

B The function receives the key only

C It causes an error

D The array is not processed

The callback can accept just the value parameter; the key is optional and ignored if not declared.

Explain how array_walk() works and how it can modify an array.

Think about how you can change each item in a list by visiting them one by one.

Compare array_walk() and array_map() in terms of modifying arrays.

Consider whether you want to change the original list or create a new one.