Loops and comparisons

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

Hello :) Consider this bit of code.

my $stri="abctest";

my @one=('a','b','c','d','e','f','g');
                                   
my $part;

my $lone=@one;                                   
my $first_char=substr($stri,0,1);   
#print "\n$first_char";
my $second_char=substr($stri,1,1);
#print "\n$second_char";
my $third_char=substr($stri,2,1);
#print "\n$third_char"; 

if ($first_char eq 'a' || $first_char eq 'b'){ 

  for(my $ne=0;$ne<$lone;$ne++){
    
    if ($second_char eq $one[$ne])  
     {                                    
    
      if ($third_char ne 'c' || $third_char ne 'd'){
       
         $part=substr($stri,0,2); 
         print "\nThe string in part:";
         print"\n$part";
        
        }
     }
  
   } 
 
}

 
if ($first_char eq 'a' || $first_char eq 'b'){ 

  for(my $ne=0;$ne<$lone;$ne++){
    
    if ($second_char eq $one[$ne]){    
    
      if ($third_char eq 'c' || $third_char eq 'd'){
                                       
        $part=substr($stri,0,3); 
        print "\nThe string in part:";
        print"\n$part";
      }
      
     }
  
   } 
 
}
[download]

When we run the above code with $stri equal to "abctest" we should get a match in the second section of loops only
i.e. if the first char in the string is 'a' or 'b' , second char is any of the elements of @one, and third char is 'c' or 'd'.
The value of part should be 'abc'.

But there is a match in both the sections of loops, and this is the output I get:

The string in part:
ab
The string in part:
abc
[download]

This comparison does not seem to be working:

if ($third_char ne 'c' || $third_char ne 'd'){
$part=substr($stri,0,2);
[download]

What is the mistake here?
Thanx :)

Comment on Loops and comparisons Select or Download Code

Replies are listed 'Best First'.
Re: Loops and comparisons by gjb (Vicar) on Oct 15, 2003 at 12:28 UTC
I'm not sure what you're after exactly, but I suppose you want the first "loop" to match when the third character is neither a 'c' nor a 'd'. Hence the condition should read `if ($third_char ne 'c' && $third_char ne 'd'){ $part=substr($stri,0,2);` [download] Incidently, there are more elegant ways to check whether `$second_char` is in `@one`. Have a look at grep, or alternatively, you can use a regexp. `my $regexStr = join("\|", @one); my $regex = qr/^$regexStr$/; ... if ($second_char =~ $regex) { ...` [download] Both approaches eliminate the need for the `for` loop. Hope this helps, -gjb-	[reply] [d/l] [select]
Re: Re: Loops and comparisons by perl_seeker (Scribe) on Oct 16, 2003 at 06:31 UTC
Hi :), using \|\| instead of && was a silly mistake.But using a regexp instead of a for loop helps, makes the code less cluttered. Thanx:)	[reply]
Re: Loops and comparisons by snax (Hermit) on Oct 15, 2003 at 13:28 UTC
You say: This comparison does not seem to be working: `if ($third_char ne 'c' \|\| $third_char ne 'd'){ $part=substr($stri,0,2);` [download] What is the mistake here? I guess it depends upon what you mean by "not working"; I assume you are aware that it is unlikely that any single character would fail to satisfy your test? :) Draw a Venn diagram :) :)	[reply] [d/l]