Could someone please explain this to me in newbie terms :)

raisputin has asked for the wisdom of the Perl Monks concerning the following question:

This one I understand fine:

# $z is $x divided by $y, unless $y is zero, in which case $z should b
+e zero too
if ( $y == 0 ) {
   $z = 0;
}
else {
   $z = $x / $y;
}
[download]

or more succinctly
$z = $y ? $x / $y : 0;

While I know that this works, I don't understand the construction. Probably because I am no brain surgeon, but hey, you don't start by performing quintuple bypasses either... :)

And I understand this even less.

and more succincly still, though thoroughly unreadable:
$z = $y && $x / $y;

Comment on Could someone please explain this to me in newbie terms :) Select or Download Code

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Re: Could someone please explain this to me in newbie terms :) by kennethk (Abbot) on Aug 07, 2009 at 18:34 UTC
A good quick reference on the operators involved can be found at perlop. Breaking down your two expressions: `$z = $y ? $x / $y : 0;` Given the ternary Conditional Operator, start with the conditional term. In Perl, `0` is equivalent to false for logical operators (as are nulls/undefs), so that term is equivalent to `$y!=0` If `$y` is not zero, the ternary returns `$x/$y` If `$y` is zero, the ternary returns `0`; Lastly, `$z` gets the value returned by `? :` `$z = $y && $x / $y;` Given the binary C style Logical And, start with the first term. If `$y == 0`, the first term is false, so return false/`0`. If `$y != 0`, the first term is true so evaluate the second term. If `$x / $y == 0`, the second term is false, so return false/`0`. If `$x / $y != 0`, the second term is true, so return true. When `&&` returns true, it returns the return value of the last expression in the chain, hence `$x / $y`. Hope that's clear...	[reply] [d/l] [select]
Re^2: Could someone please explain this to me in newbie terms :) by Anonymous Monk on Aug 08, 2009 at 08:32 UTC
To be explicit, `$z = $y && $x / $y;` construct assigns the value of `$y` to `$z`, not necessarily a zero unlike `$z = $y ? $x / $y : 0;`.	[reply] [d/l] [select]
Re^3: Could someone please explain this to me in newbie terms :) by Anonymous Monk on Aug 08, 2009 at 09:47 UTC
... when `$y` evaluates to a false truth value.	[reply] [d/l]
Re: Could someone please explain this to me in newbie terms :) by moritz (Cardinal) on Aug 07, 2009 at 18:24 UTC
First you have to understand that when you ask `if ($y) { ... }` and `$y` is a number, than this is short for `if ($y != 0) { ... }`. The `? :` construct is like a short `if` which returns a value: if the condition is true, the value of the expression between ? and : is evaluated, if not, the expression after the : is evaluated (and returned).	[reply] [d/l] [select]
Re: Could someone please explain this to me in newbie terms :) by raisputin (Scribe) on Aug 07, 2009 at 20:09 UTC
Thanks guys, that makes sense now :)	[reply]