Will multiple conditionals slow down page load?

Question

I plan to implement some specific content for specific categories only, about 15. I wonder will wordpress conditionals (15 if) slow down my website visibly? Sorry if this sounds silly.

Answer 1

The answer is no but just to put your question into perspective I tried the following code. 1.5 million ifs.

$start = microtime();
$count = 0;
while(true) {
    $count++;
    if($count > 1500000) {
        break;
}
}
$stop = microtime();

$total = $stop-$start;
print "Total time:$total";

0.16 seconds

Answer 2

Conditional Tags are basically just short wrapper functions for parts of the global $wp_query;.

Example: is_author();

function is_author( $author = '' ) {
    global $wp_query;

    if ( ! isset( $wp_query ) ) {
        _doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1' );
        return false;
    }

    return $wp_query->is_author( $author );
}

And this ↑ just retrieves a class var from the WP_Query object. That's it. So: No, they can't really add any noticeable overhead (unless you don't get millions of synchronous hits). Not more than interacting with any other object.