How to loop through an associative array and get the keys in PHP

If I have an associative array: 

$arr = array(
   1 => "Value1",
   2 => "Value2",
   10 => "Value10"
);

then I want to get the keys "1", "2" and "10" of the array $arr?

there are may approach to do first we should use foreach() loop with key and value then echo the keys,

foreach ($arr as $key => $value) {
 echo $key;
}

Another use array_keys(), PHP will give you an array filled with just the keys:

$keys = array_keys($arr);
foreach($keys as $key) {
    echo($key);
}

#complete_example.php

<?php
$arr = array(
   1 => "Value1",
   2 => "Value2",
   10 => "Value10"
);

foreach ($arr as $key => $value) {
 echo $key;   //output 1 2 10
}

?>

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