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

Hello, I am trying to prompt a user to enter a key, then use the input to display the value with that key. I can get key but unable to get the value. Here is my code: 
### create a hash
my %fruit_num = ( apple => 3,
                  bananas => 1,
                  oranges => 2,
                  );


### promp the user to enter a key
### use the input to display the value with that key.

print "Which fruit do you wish to query? ";
my $fruit = <STDIN>;
my $fruits = $fruit_num{$fruit};

chomp $fruit;

print "Number of" . $fruit . " is " .  $fruits . "\n";

[download]
I know the problem is where I need to get the value, but I am not sure how to fix it. If any one can help me I would appreciate it. Thank you for your time. Randy

Replies are listed 'Best First'.
Re: Hash from prompt
by Athanasius (Archbishop) on Oct 13, 2014 at 04:01 UTC

    Hello rshoe, and welcome to the Monastery!

    You’re nearly there! You just need to move the line:

    chomp $fruit;

    [download]

    to before the line:

    my $fruits = $fruit_num{$fruit};

    [download]

    in which you access the hash. Why? After $fruit has been assigned the user’s input, its final character is a newline. With the newline still present, the hash lookup fails because the key apple\n is not the same as the key apple. chomp removes the trailing newline, so the user’s input then matches a hash key, and the hash lookup succeeds.

    Hope that helps,

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

[reply]
[d/l]
[select]
      Athanasius: Thanks for your quick reply. The information you gave me makes sense. I made the change but I get an error that states: "Use of uninitialized value $fruits in concatenation (.) or string at asstl.pl line 28, <STDIN> line 1. Here is my updated code: 
      ### create a hash
my %fruit_num = ( apple => 3,
                  bananas => 1,
                  oranges => 2,
                  );

### promp the user to enter a key
### use the input to dispaly the value with that key.

print "Which fruit do you whish to query? ";
my $fruit = <STDIN>;
chomp $fruit;

my $fruits = $fruit_num{$fruit};

print "Number of" . $fruit . "is" . $fruits . " \n";

      [download]
      I have even tried taken out the concatenation on the print line but still get an error. Any help would be appreciated. Randy
[reply]
[d/l]

        You’re welcome. Here is a more robust version of the script which uses exists to test that the fruit entered is present as a key in the hash before trying to access its corresponding value:

        #! perl
use strict;
use warnings;

my %fruit_num =
(
    apples  => 3,
    bananas => 1,
    oranges => 2,
);

print "Which fruit do you wish to query?\n";
my    $fruit = <STDIN>;
chomp $fruit;

if (exists $fruit_num{$fruit})
{
    my $fruits = $fruit_num{$fruit};
    print "Number of $fruit is $fruits\n";
}
else
{
    print "No data for fruit '$fruit'\n";
}

        [download]

        Typical runs:

        14:35 >perl 1055_SoPW.pl
Which fruit do you wish to query?
apples
Number of apples is 3

14:35 >perl 1055_SoPW.pl
Which fruit do you wish to query?
guavas
No data for fruit 'guavas'

14:36 >

        [download]

        Hope that helps,

        Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

[reply]
[d/l]
[select]
        Athanasius: I just figured out what I did wrong. I typed in the wrong key. Everything works now. I appreciate all your help. Thank you; Randy
[reply]

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