Selecting a specific hash key to find a value

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

Hello! I just started to learn perl a few weeks ago using the O'Reilly books so please bare with this simple question.

I am using Visual Studio (with the Perl mod from activestate) to write this code to work in windows.

The following code is a piece of a larger program. I want to ask the user for a number and use that as the key to pull a value out of the hash. But I have not been successful. Her is the code below:

#!/usr/bin/perl
print "Give me a number for the tile and I will tell you the color\n";
$a=<STDIN>;
print $a."\n";
%Number = qw(1 Red
    2 Yellow
    3 Green 
    4 Black 
    5 Purple 
    6 Pink 
    7 Brown 
    8 Blue 
    9 Orange);

print $Number{$a}."\n";
[download]

The strange thing is when I set $a to a value in the code (ie $a=5 instead of <STDIN>) I get the correct answer. Any ideas?!! And thanks in advance for your help!!

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Re: Selecting a specific hash key to find a value by zejames (Hermit) on Sep 23, 2004 at 16:57 UTC
Your have to chomp the variable, that is remove the trailing \n : `#!/usr/bin/perl print "Give me a number for the tile and I will tell you the color\n"; chomp($a=<STDIN>); print $a."\n"; %Number = qw(1 Red 2 Yellow 3 Green 4 Black 5 Purple 6 Pink 7 Brown 8 Blue 9 Orange); print $Number{$a}."\n";` [download] BTW, your code will be cleaner if you construct your hash like this : `%Number = (1 => 'Red', 2 => 'Yellow', 3 => 'Green');` [download] It'll be clearer that you are using a hash table. On the other way you could use a array for that : `@Number = ('Red', 'Yellow', 'Green'); print $Number[$a]."\n";` [download] That is much more logical, as your keys are consecutive numbers. Hash a usually used when keys are strings or more complicated objects. -- zejames	[reply] [d/l] [select]
Re: Selecting a specific hash key to find a value by Sidhekin (Priest) on Sep 23, 2004 at 17:02 UTC
Your `$a=<STDIN>` leaves $a containing for instance `"5\n"`, that is, including the newline. If you just `chomp($a)` your code would work. Unless there were trailing spaces or stuff ... Better to use `$a+=0;` to make it numeric. Oh, and as the monks are sure to be telling you: You should not use `$a` outside of `sort`, since that is a special variable there. `print "Just another Perl ${\(trickster and hacker)},"` The Sidhekin proves Sidhe did it!	[reply] [d/l] [select]
Re: Selecting a specific hash key to find a value by Eimi Metamorphoumai (Deacon) on Sep 23, 2004 at 17:04 UTC
zejames is right, but I'd also like to mention that if you're just using a hash to map consecutive integers to values, you might want to consider using an array instead. It can make it a lot easier to modify your values later (say, adding an item into the middle without renumbering everything manually). `#!/usr/bin/perl print "Give me a number for the tile and I will tell you the color\n"; chomp($a=<STDIN>); print $a."\n"; @Number = qw(Red Yellow Green Black Purple Pink Brown Blue Orange); print $Number[$a-1]."\n";` [download]	[reply] [d/l]
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