The in_array() function is an predefined function in PHP. The in_array() function is used to check whether a given value exists in an array or not. If the value exist in the array its return true otherwise return false.
<?php
$roll_number = array(1,2,3,4,5 );
if (in_array("2", $roll_number))
{
echo "found";
}
else
{
echo "not found";
}
?>