#!/usr/bin/perl -w

use strict;

my @tag_a;
my @pos_i1;
my @pos_i2;
my @name;

my $datei;
my $tr_id;
my $zeile;
my $zeile_1;
my $p1;
my $p2;
my $id;
my $i;
my $itag;
my $ok;
my $max_i;
our $plus;
my $k;

...

open (IN,"<$datei") || die $!;
while(<IN>){
        ...
	$plus = 0;
	
	while($i <= $max_i - 1){
              ...
		if ($zeile eq $tag_a[$i]){
                     ...
			SWITCH: {
  			$i == 0 && do { print "$name[$i]:           $_";
		  		 							last SWITCH; };			
  			$i == 1 && do { $plus = -1;
  											print "$i     Plus: $plus\n";
  											last SWITCH; };
=====> 			$i == 2 && do { print "=====> $i          $plus\n";
  											$k = $i + $plus;
  											print "$k    $name[$k]:           $_"; 
  											last SWITCH; };
  			$i == 3 && do { print "$name[$i]:           $_"; 
  											last SWITCH; };
  		print "\$i is not in 0..3\n";
			}	
			$i = $i + 1;		
		}
		else {
			$i = $i + 1;
		}	
	} 
}
close IN;