use of uninitialized value

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

Hi monkers, Iam back with a struggle trying to subtract elements from two columns and different rows in a array. I have my TSV file as input that has two of my columns. and want to subtract the 0th value of my 2nd column with the 1st value of the 1st column. then again go on subtracting this this way till the end of the column. I tried to put the data into two array and applied the subtraction operator but i am getting error as "use of uninitialized value in subtraction" and there is no output in my file but the size has increased. The code i used is below, and i have no idea where i went wrong! please help.

open (FILE, 'probe_dist.tsv');
open (OFILE,'>probe_sum.tsv');
while (<FILE>)
{
    my @a;
    my @b;
    ($a,$b)=split ("\t");
    $a=@a;
    $b=@b;
    my $c;
    my $d;
    my $c=1;
    my $d=0;
    my $e=$b[$d]-$a[$c];
    $c++;
    $d++;
    print OFILE "$e\n";
    
}
[download]

my input file looks like this

4775792 4775851
4775842    4775901
4775852    4775911
4775902    4775961
4775952    4776011
4776002    4776061
4776052    4776111
4776102    4776161
4776212    4776271
4776252    4776311
4776302    4776361
4776352    4776411
[download]

Comment on use of uninitialized value Select or Download Code

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Re: use of uninitialized value by Anonymous Monk on Jul 01, 2013 at 06:53 UTC
The code i used is below, and i have no idea where i went wrong! please help. Sure you do, perl told you a linenumber :) my tips , `use autodie;` so it error checks your open/close calls And strict/warnings ( Read this if you want to cut your development time in half! ) And use meaningful variable names (words not letters) Then employ Basic debugging checklist and/or brian's Guide to Solving Any Perl Problem to figure out which variable is uninitialized and why it happens (basically `warn Dumper( ... );` ) Then you'll have a better idea of where you're going wrong, and then you can think of strategies to fix it; for example, expanding the scope of some of these variables you want to reuse ( Lexical scoping like a fox ) If you're game, I'm game ; I'll play if you'll play	[reply] [d/l]
Re: use of uninitialized value by farang (Chaplain) on Jul 01, 2013 at 07:26 UTC
The advice of Anonymous Monk above is all excellent, but this for one thing will not fly. `($a,$b)=split ("\t"); $a=@a; $b=@b;` [download] Whatever you have in `$a` and `$b` after the split is immediately turned to 0 by assigning empty arrays to those variables.	[reply] [d/l]
Re: use of uninitialized value by hdb (Monsignor) on Jul 01, 2013 at 09:16 UTC
You seem to want to populate the arrays `@a` and `@b` with the data from your file. But you declare them within the loop over the lines of your file. So for every line you read you create new versions of these arrays and forget all information from previous lines. This is surely not what you want. To make your data persistent across the lines of your file, you need to declare common structures before you enter the loop. `my @a; my @b; while (<FILE>) { ...` [download]	[reply] [d/l] [select]