How to get file extension in php

$pic = 'abc.3434.342.12123.123.exe';
$pics = explode('.' , $pic);
< p>/*Get the total number of the array, and then take the last one*/
echo $num = count($pics);
echo ''.$pics[$num-1];
< ;p>/*Traverse the array and get the last element*/
foreach ($pics as $value) //2
{
$a = $value;
}
echo $a.'';
 /*Directly output the last element of the array*/
echo end($pics);
echo '';
/*Single out the last element of the array, pay attention to the difference with end()*/
//echo array_pop($pics);
/*First sort the array in reverse order by key value, and then single out the first element*/
krsort($pics);
echo array_shift($pics);
echo '' ;
/*The value corresponding to the extension index of the pathinfo() function return value*/
$res = pathinfo($pic); //5
var_dump($res);
echo $ res['extension'].'';
/*String interception, just take the last three digits*/
echo substr($pic, -3, 3) ;
?>