PHP中的单引号和双引号字符串有什么区别？

Question

I am just beginning to learn PHP and I am using PHP for the Web: Visual Quickstart Guide 4th edition and I have a question about a script I learned in the book and just wrote.

This is the code of the script:

     print '<p>Thank you, ' .$title.$name. ' for your comments.</p>
    <p>You stated that you found this example to be "'.$response.'" and added:<br />'
    .$comments.'</p>';

    print "<p>Thank you, $title $name for your comments.</p><p>You stated that you found this example to be '$response' and added:<br/>$comments</p>";

This script is just displaying some data from an HTML form that is pulled via POST.

What is the correct way to do this? I am having a lot of trouble understanding ' vs " in this context.

The second example is the one out of the book and the first example is one that I found how to do after trying to understand the ' vs " question. In regards to this, where is a good location to find information about ' vs ".

Answer 1

Double quoted strings get parsed by the PHP parser for variables and escaped characters like

$x = 10;
echo "$x dollars"; // Outputs: 10 dollars

Single quoted strings do not get parsed so:

$x = 10;
echo '$x dollars'; // Outputs: $x dollars

and to output 10 dollars you would need to do string concatenation:

$x = 10;
echo $x.' dollars';

Parsing variables within strings uses more memory and takes more time than string concatenation. So single quotes are almost always the better way to go. Even though the difference is small.