[SOLVED] comparing 2 numbers and swapping values via greater/less than value.

[boo_lolly]

i know this is feasible i just can't remember how to do it! let's say i have 2 variables and their values will always be a positive number, except $var1 needs to be compared to $var2 to see which one is greater than the other. i need a function that will run some comparisons and the end result would be to return $var1 as the smaller of the two, and $var2 as the larger one. the trick is to only use 2 variables: $var1 and $var2. i've come up with a few things but none of them work. just a basic debugger for the foundation of this function i have:

<?php
        $first = 10;    $second = 2;
        (($first < 0) ? ($first *= -1) : (''));
        (($second < 0) ? ($second *= -1) : (''));
        echo "First = {$first}<br />\n";
        echo "Second = {$second}<br />\n";

        $second -= $first;
        echo "[\$second -= \$first] is {$second}<br />\n";

        echo "First = {$first}<br />\n";
        echo "Second = {$second}<br />\n";
?>

 

where i'm trying different variations of processing to the variables and printing out the operation in text, then giving the result. i know there's a way to do this without having to use a third variable in just a few lines of code. can anyone help me?

[Glyde]

If you want to know which one has the greater absolute value (offset from 0) then it's simple:

<?php
function greatestNum($first, $second) {
     return abs($first) < abs($second) ? array($second, $first) : array($first, $second);
}
print_r(greatestNum(10, -100));
?>

Should output:

Array (

  [0] => -100

  [1] => 10

)

Because -100 is further away from 0 than 10 is.

[boo_lolly]

i know how to determine which one has the greater value. what i want to do is replace the value of $var1 with the value of $var2 if the value of $var1 is greater than $var2. but, i want the original value of $var2 to be the previous value of $var1. again, without using anymore variables than $var1 and $var. make sense?

 

btw i was wondering if there was an absolute value function but i didn't think any further than that, i just wrote that one line to do it. so, thanks for illustrating that point, bud.

[Glyde]

You can try this:

<?php
function swapGreater(&$first, &$second) {
     list($first, $second) = $first < $second ? array($second, $first) : array($first, $second);
}
?>

But I'm not sure if it'll work in PHP 4, or even PHP 5 for that matter...as it's untested.

[boo_lolly]

that wasn't really what i was going for, but i '<' changed to '>' and it worked perfectly and i'm going to use it. hrere's the finished func:

<?php
        function swapGreater(&$first, &$second){
                $first = abs($first);   $second = abs($second);
                list($first, $second) = $first > $second ? array($second, $first) : array($first, $second);
        }
?>

 

btw i'm running PHP 4. to be honest i was look for something like:

<?php
        if($first > $second){
                $first -= $second;
                $second += $first;
        }
?>

 

or something similar. i don't know how to do it but i've seen it done before. i was just trying to see if anyone can help me understand how to do that. also, thank you for illustrating what '&' does. i've seen it every now and then in front of variables but i had no idea why people used it or what it's purpose was. i can see now it allows you to store it in an array, right? thanks again bro.

[Moon-Man.net]

Hey! Sorry to but in on this thread, what does += and -= do to the vars? And I've never seen PHP layed out like this:

<?php
        function swapGreater(&$first, &$second){
                $first = abs($first);   $second = abs($second);
##              list($first, $second) = $first > $second ? array($second, $first) : array($first, $second);
        }
?>

 

Specifically the line with the two hashes... Is there somewhere I can read on how to do this? It looks like a really good and solid way of doing things....

-- Nathan

[boo_lolly]

to explain your first question:

<?php
        $var += 5;
        //is the same as...
        $var = $var + 5;

        $var -= 2;
        //is the same as...
        $var = $var - 2;

        //same goes for '*' and '/'
?>

make sense?

 

and as for the hashed out line you posted. it's just another way of doing an if/else statement.

 

so these:

<?php
        $first < $second ? do_something : do_something_else;
        ($first < $second) ? (do_something) : (do_something_else);
        (($first < $second) ? (do_something) : (do_something_else));
?>

 

are all exactly the same as this:

<?php
        if($first < $second){
                do_something;
        }else{
                do_something_else;
        }
?>

 

there is no difference.

[Moon-Man.net]

Awesome, Thanks mate! That's really handy, I've just never seen it layed out like that. Its a lot simpler to write. But a little more complicated to read. But I guess if you know what your doing its ok and nice and neat

I'll let this thread get back to its original question. Sorry for hijacking

Thanks again..

-- Nathan

[dwees]

Try this:

 

$var1 = ($var1 <= $var2) ? $var1 : $var2;
$var2 = ($var2 > $var1) ? $var2 : $var1;

 

 

[Glyde]

that wasn't really what i was going for, but i '<' changed to '>' and it worked perfectly and i'm going to use it. hrere's the finished func:

<?php
        function swapGreater(&$first, &$second){
                $first = abs($first);   $second = abs($second);
                list($first, $second) = $first > $second ? array($second, $first) : array($first, $second);
        }
?>

 

btw i'm running PHP 4. to be honest i was look for something like:

<?php
        if($first > $second){
                $first -= $second;
                $second += $first;
        }
?>

 

or something similar. i don't know how to do it but i've seen it done before. i was just trying to see if anyone can help me understand how to do that. also, thank you for illustrating what '&' does. i've seen it every now and then in front of variables but i had no idea why people used it or what it's purpose was. i can see now it allows you to store it in an array, right? thanks again bro.

Actually & creates a reference to the original variable.  Here's an example:

 

<?php
$var1 = "Some Text";
$var2 = &$var1;
$var1 = "Some other text";
print $var2;
?>

While most people not knowing what & meant would expect this to print Some Text, it actually prints Some other text, since $var2 is simply a pointer to $var1