if... else... & elseif

[royal1664]

Hi, since learning PHP i've come across this and i'm a little confused. Was wondering if anyone could shed some light on it.

 

I'm more than familiar with IF statements from C++. However i'm confused as to why you might use an ELSEIF...

 

why does it not work like this (below)?

IF(This is true)
{
do this
}

IF(this is true)
{
do this
}

IF(this is true)
{
do this
}

else
{
go home, you're drunk
}

I don't under stand why if you make the first IF statement every other IF statement has to be an ELSEIF.

 

Many thanks,

Royal1664

[AbraCadaver]

From your example I don't understand what you don't understand: http://us2.php.net/elseif

if ($a > $b) {
    echo "a is bigger than b";
} elseif ($a == $b) {
    echo "a is equal to b";
} else {
    echo "a is smaller than b";
}

[Zane]

elseif extends the beginning IF statement so that you can have more conditions...

 

Otherwise, you would end up checking any and all conditions one by one which means that more than one can be true..

 

With an elseif chain.... only one will be true.

[kicken]

You can use several if's like you showed, but it will not necessarily do as you intended. When you do several if's as shown, then they are all evaluated independantly. Depending on what the condition is that you check, it may emulate the same behaviour as using elseif.

 

When you use elseif, then everything is treated as a single block so only one of the if statements (or else block) can be evaluated, all others are skipped.

 

Take for example:

$x = 52;
if ($x < 100){
   echo '< 100';
}
else if ($x < 75){ 
   echo '< 75';
}
else if ($x < 50){
   echo '< 50';
}
else {
   echo 'None of the above';
}

The output of that would be '< 100'. Since that if condition matches, all other elseif's and the else block are skipped.

 

If however you wrote them as separate statements such as

$x = 52;
if ($x < 100){
   echo '< 100';
}
if ($x < 75){ 
   echo '< 75';
}
if ($x < 50){
   echo '< 50';
}
else {
   echo 'None of the above';
}

You would get the output '< 100< 75None of the above' since each if is evaluated separately. The first if passes, the second if passes, the third doesn't pass so it's associated else block gets executed.

[KevinM1]

AFAIK, if/else in PHP is the same as it is in C++ (which makes sense since PHP is written, I believe, in C). While C++ doesn't have a dedicated elseif language construct, it's very common to see

 

else if (/* something */) in C++. If it helps, just turn elseif into:

 

if (/* something */) {
    // blah
} else {
    if (/* something else */) {
        // blah
    }
}

[royal1664]

Nice one, thanks mate!