Using PHP variables inside HTML tags?

Well, for starters, you might not wanna overuse echo, because (as is the problem in your case) you can very easily make mistakes on quotation marks.

This would fix your problem:

echo "<a href=\"http://www.whatever.com/$param\">Click Here</a>";

but you should really do this

<?php
  $param = "test";
?>
<a href="http://www.whatever.com/<?php echo $param; ?>">Click Here</a>

You can do it a number of ways, depending on the type of quotes you use:

• echo "<a href='http://www.whatever.com/$param'>Click here</a>";
• echo "<a href='http://www.whatever.com/{$param}'>Click here</a>";
• echo '<a href="http://www.whatever.com/' . $param . '">Click here</a>';
• echo "<a href=\"http://www.whatever.com/$param\">Click here</a>";

Double quotes allow for variables in the middle of the string, where as single quotes are string literals and, as such, interpret everything as a string of characters -- nothing more -- not even \n will be expanded to mean the new line character, it will just be the characters \ and n in sequence.

You need to be careful about your use of whichever type of quoting you decide. You can't use double quotes inside a double quoted string (as in your example) as you'll be ending the string early, which isn't what you want. You can escape the inner double quotes, however, by adding a backslash.

On a separate note, you might need to be careful about XSS attacks when printing unsafe variables (populated by the user) out to the browser.