letters++, bug or trick?

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

Replies are listed 'Best First'.
Re: letters++, bug or trick? by BrowserUk (Patriarch) on Jan 30, 2010 at 07:21 UTC
It's all perfectly logical really. The first thing to notice is that the initialisation of `$c` makes no difference to the outcome: `perl -e "$c=qq(z);$d=qq(d); $c = $d++; $d = $c++; print $c,$d;" ed perl -e "$d=qq(d); $c = $d++; $d = $c++; print $c,$d;" ed` [download] So, `$d` is set to 'd' `$c` is set to `$d` ('d') `$d` is incremented ('e') `$d` is set to `$c` ('d') `$c` is incremented ('e') 'ed' is printed. In the end, the whole thing reduces to: `perl -e "$d=qq(d); $c = $d; $d = $c++; print $c,$d;" ed` [download] or even just `perl -e "$c = $d = qq(d); $c++; print $c,$d;" ed` [download] Which looks a lot less mysterious :) Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "I'd rather go naked than blow up my ass"	[reply] [d/l] [select]
Re^2: letters++, bug or trick? by xiaoyafeng (Deacon) on Jan 30, 2010 at 07:51 UTC
Ah! too much ++ confused me! the last statment is really a concise answer! thanks! I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction	[reply]
Re: letters++, bug or trick? by biohisham (Priest) on Jan 30, 2010 at 08:12 UTC
This is not a bug nor a trick neither, the ++ operator works on strings stored in scalar variables as long as they have never been used in a numeric context, once these variables are used in a numeric context a re-initialization of the variable's value into a number takes place.. `#!/usr/local/bin/perl $c = "c"; print ++$c," from c\n"; print ++$c," from d\n"; #apply the same in numeric context $c+=0; print $c, " from numeric operation\n"; print ++$c, " incremented after numeric assignment";` [download] However, Perl would throw a warning when it reaches to "`$c+=0;`" telling you that a non-numeric argument is used in the addition operation if you have turned warnings on via "`use warnings`" which can save you from introducing a potentially hard-to-track bug otherwise... Excellence is an Endeavor of Persistence. Chance Favors a Prepared Mind.	[reply] [d/l] [select]