Comments often require no more than a single line. Because of its brevity, there is no need to delimit the
comment’s conclusion because the newline \n character fills this need quite nicely. PHP supports C++
single-line comment syntax, which is prefaced with a double slash //, like this:

<?php
    echo 'This is a test'; // This is a one-line c++ style comment
    /* This is a multi line comment
       yet another line of comment */
    echo 'This is yet another test';
?> 

PHP also supports an alternative to the C++-style single-line syntax, known as shell syntax, which is
prefaced with a hash mark #. Revisiting the previous example, I’ll use hash marks to add some
information about the script:

<?php
# Title: My first PHP script
echo "This is a PHP program.";
?>

It’s often convenient to include somewhat more verbose functional descriptions or other explanatory
notes within code, which logically warrants numerous lines. Although you could preface each line with
C++ or shell-style delimiters, PHP also offers a multiple-line variant that can open and close the
comment on different lines. Here’s an example:

<?php
/**
 * this is comment
 * this is comment agian
 */
?>