Re: Learning Perl - Question About Using a For Loop To Pull Data From an Array

Well for one, this line $counter = @userNumber; causes the value of $counter to be set to the number of elements in @userNumber. This is the same as $counter = scalar @userNumber;

The foreach loop loops over the contents of @userNumber. Change print $counter; to print "@userNumber\n"; to see the contents of @userNumber instead of the number of things in @userNumber.

Update: looks like some issues here also: @userNumber = <STDIN>; You need a loop here to push the number entered by the user to @userNumber. CTL-D is an EOF. So something like this should work: while (<STDIN>){push @userNumber, $_);}. I didn't run your code, but I think the above will solve a couple of issues. another Update: I did run the code and well @userNumber = <STDIN>; does indeed work. It just looked weird to me as I never use CTL-D (or CTR-Z on Windows) to terminate user input. But a while loop is the right kind of loop because as you write more code, you will want to end the loop on a blank line or some other thing like zero and that condition will go in the while statement. Users don't do well with control characters.

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Re^2: Learning Perl - Question About Using a For Loop To Pull Data From an Array by GotToBTru (Prior) on Apr 01, 2016 at 19:40 UTC
No, you don't need a loop to create the array. The OP indicated that the program worked, only that he did not understand why. The ctrl-D does indicate this should be run in a *nix environment, not a Windows one. I'm with you in that I would never write it this way. But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Romans 5:8 (NASB)	[reply]
Re^2: Learning Perl - Question About Using a For Loop To Pull Data From an Array by aUserName (Initiate) on Apr 01, 2016 at 18:26 UTC
Thank you for your reply. As you mentioned the script works fine. This is an example from a textbook which is why it may seem odd and not look like a real world script. I am not having any issues with the code, rather I am trying to understand how the for loop is using the $counter variable to pull out the actual number that user entered when it appears that $counter is being used as a scalar. For example if the user enters 1 and 3 they get fred and barnet back which are the first and third items in the array respectively. What is confusing me is why is $names $counter - 1 giving the correct values back. If the user enters 2 values, such as 1 and 3, $counter would = 2, not 1 or 3 since it is being treated as a scalar. Yet the script correctly returns the 1st and 3rd item in the array instead of the the 1st and 2nd item of the array. Thank you for your help.	[reply]
Re^3: Learning Perl - Question About Using a For Loop To Pull Data From an Array by NetWallah (Canon) on Apr 01, 2016 at 18:44 UTC
It seems that the name chosen, $counter, is confusing you. It is being used as an INDEX, rather than as a traditional COUNTER. The array is indexed from 0 to (n-1). (Updated to n-1)(Thanks, Corion) You need to subtract one from the value entered, in order to get the equivalent index for a zero-based array. Hopefully, that clarifies things. FYI, Fred's friend is named Barney, not barnet. and Barney's kid is Bamm-Bamm. This is not an optical illusion, it just looks like one.	[reply]
Re^3: Learning Perl - Question About Using a For Loop To Pull Data From an Array by Marshall (Canon) on Apr 01, 2016 at 20:33 UTC
What this `foreach $counter (@userNumber){}` does is assign $counter to each value in the array @userNumber. It does this on a first in, first out basis. If the user entered say 1,3,2.. The first loop $counter = 1, then $counter =3, then on last loop, $counter = 2. Before `print "\nthe name is: $names[$counter - 1]`, add a statement, `print "counter = $counter\n";`. And you can see what counter is. Use some non-sequential test cases. Part of the problem here is a rather poor choice of names for "counter". $name_number or something similar would have been better. There is no "count" function of $counter! It is being used as a 1 based index to the names array. Perl starts arrays at 0, not one, so that is what $counter-1 is all about. Hopefully that makes sense?	[reply] [d/l] [select]