What's the difference between if and elseif?

Question

This should be a simple question. I have a simple if/else statement:

    <?php
    // TOP PICTURE DEFINITIONS
    if ( is_page('english') ) {
        $toppic = 'page1.png';
    }
    if ( is_page('aboutus') ) {
        $toppic = 'page1.png';
    }
    if ( is_page('newspaper') ) {
        $toppic = 'page1.png';
    }
    else {
        $toppic = 'page1.png';
    }
?>

Is there a difference from ^^^ to this:

<?php
    // TOP PICTURE DEFINITIONS
    if ( is_page('english') ) {
        $toppic = 'page1.png';
    }
    elseif ( is_page('aboutus') ) {
        $toppic = 'page1.png';
    }
    elseif ( is_page('newspaper') ) {
        $toppic = 'page1.png';
    }
    else {
        $toppic = 'page1.png';
    }
?>

I should mention that this is going into Wordpress. And until now, I've used the first part (no elseif, just a series of 'ifs'), and it works. I was just curious to know what the difference was.

Thanks! Amit

Answer 1

Yes. If a condition in an if/else control is satisfied, the rest of the checks will be omitted. else if is just a nested if inside an else!

if ( is_page('english') ) { // if true, other statements are skipped
    $toppic = 'page1.png';
}
elseif ( is_page('aboutus') ) {
    $toppic = 'page1.png';
}
elseif ( is_page('newspaper') ) {
    $toppic = 'page1.png';
}
else {
    $toppic = 'page1.png';
}

But in a series of ifs, all of them will be tested.

if ( is_page('english') ) {
    $toppic = 'page1.png';
}
if ( is_page('aboutus') ) { // will be tested no matter what the outcome
                            // of the previous if statement was
    $toppic = 'page1.png';
}
if ( is_page('newspaper') ) { // the same here
    $toppic = 'page1.png';
}
else {
    $toppic = 'page1.png';
}

So, if you're checking a property such as parity of a number, it's either odd or even, why do you want to bother checking other conditions if one is satisfied. It's a waste of resources. Therefore, the following code is much better

if(number_is_odd) {
}
else { // if it's not odd, it's even for sure
}

than

if(number_is_odd) {
}

if(!number_is_odd) {
}

Because the former checks the condition once whilst the latter does it twice. The same thing goes for conditions with more than two states.