Difference between "as $key => $value" and "as $value" in PHP foreach

Question

I have a database call and I'm trying to figure out what the $key => $value does in a foreach loop.

The reason I ask is because both these codes output the same thing, so I'm trying to understand why it's written this way. Here's the code:

1)In foreach use $key => $value

foreach($featured as $key => $value){   echo $value['name']; } 

this outputs the same as:

2)In foreach use only $value

foreach($featured as $value) {   echo $value['name']; } 

So my question is, what is the difference between $key => $value or just $value in the foreach loop. The array is multidimensional if that makes a difference, I just want to know why to pass $key to $value in the foreach loop.

Answer 1

Well, the $key => $value in the foreach loop refers to the key-value pairs in associative arrays, where the key serves as the index to determine the value instead of a number like 0,1,2,... In PHP, associative arrays look like this:

$featured = array('key1' => 'value1', 'key2' => 'value2', etc.); 

In the PHP code: $featured is the associative array being looped through, and as $key => $value means that each time the loop runs and selects a key-value pair from the array, it stores the key in the local $key variable to use inside the loop block and the value in the local $value variable. So for our example array above, the foreach loop would reach the first key-value pair, and if you specified as $key => $value, it would store 'key1' in the $key variable and 'value1' in the $value variable.

Since you don't use the $key variable inside your loop block, adding it or removing it doesn't change the output of the loop, but it's best to include the key-value pair to show that it's an associative array.

Also note that the as $key => $value designation is arbitrary. You could replace that with as $foo => $bar and it would work fine as long as you changed the variable references inside the loop block to the new variables, $foo and $bar. But making them $key and $value helps to keep track of what they mean.

Answer 2

Let's say you have an associative array like this:

$a = array(     "one" => 1,     "two" => 2,     "three" => 3,     "seventeen" => array('x'=>123) ); 

In the first iteration : $key="one" and $value=1.

Sometimes you need this key ,if you want only the value , you can avoid using it.

In the last iteration : $key='seventeen' and $value = array('x'=>123) so to get value of the first element in this array value, you need a key, x in this case: $value['x'] =123.