Re: Good Perl book?

Hi all

Thank you for your responses. I just tried the following. Took me a few searches, I also happened to get the brackets wrong for the array....used [ instead of (... and then went "heck, [ is for anonymous arrays..." hahaha. The map and grep took google searches to get it flowing back.

C:\>more first.pl
#use warnings;
#use strict;
my @arr = (1..10);
foreach my $num (@arr) {
        print "Index is: $num. Value is: $arr[$num] ";
}
#Another way
print "\nWith a C like for loop\n";
 for($num = 0; $num<= $#arr;$num++) {
         print "Index is: $num. Value is: $arr[$num] ";
}

my @divbytwo =  map { $_ / 2} @arr;
print "\n\@divbytwo = @divbytwo\n";

my @divbytwoo =  grep { $_ % 2 == 0} @arr;
print "\@divbytwoo = @divbytwoo\n";

C:\>perl first.pl
Index is: 1. Value is: 2 Index is: 2. Value is: 3 Index is: 3. Value i
+s: 4 Index is: 4. Value is: 5 Index is: 5. Value is: 6 Index is: 6. V
+alue is: 7 Index is: 7. Value i
s: 8 Index is: 8. Value is: 9 Index is: 9. Value is: 10 Index is: 10. 
+Value is:
With a C like for loop
Index is: 0. Value is: 1 Index is: 1. Value is: 2 Index is: 2. Value i
+s: 3 Index is: 3. Value is: 4 Index is: 4. Value is: 5 Index is: 5. V
+alue is: 6 Index is: 6. Value i
s: 7 Index is: 7. Value is: 8 Index is: 8. Value is: 9 Index is: 9. Va
+lue is: 10
@divbytwo = 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
@divbytwoo = 2 4 6 8 10
[download]

I think I better start from scratch :)

Comment on Re: Good Perl book? Download Code

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Re^2: Good Perl book?
by Athanasius (Archbishop) on Feb 11, 2017 at 02:45 UTC

This is actually pretty close to what you wanted. Un-comment use warnings and the resulting message will help to identify the problem:

Use of uninitialized value in concatenation (.) or string at first.pl 
+line 5.
[download]

The problem loop is:

foreach my $num (@arr) {
        print "Index is: $num. Value is: $arr[$num] ";
}
[download]

and as the output shows, the loop value is always one greater than the index. That’s because arrays in Perl (as in C) are subscripted starting from zero, so $arr[1] is actually the second element. The loop is easily fixed:

foreach my $num (@arr) {
        print "Index is: $num. Value is: $arr[$num - 1] ";    # Subtra
+ct 1 from the index
}
[download]

Also un-comment use strict, and you’ll see that the only error message pertains to this line:

for($num = 0; $num<= $#arr;$num++) {
[download]

Declare $num as a lexical variable:

for (my $num = 0; ...
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and strict is happy.

Hope that helps,

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

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Re^3: Good Perl book?

by Anonymous Monk on Feb 11, 2017 at 02:58 UTC

Thank you for your patience and guidance. It was stupid of me to comment it out. Perl and perlmonks are awesome. Respect.

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