Your for loop is giving testing everything after @dna[4], not every third one, as the $i is only being incremented by one each time through the loop. i.e.
Wasn't sure how to explain but here are the values of $i and $i + 3 each time through the loop:
,etc...

I think what you are looking for is something more along these lines (as a for loop):


for ( my $i = 2; $i < @dna; $i = $i+3 )
{
  print "$dna[$i] at position $i\n";
  if ( $dna[$i]  eq 'C' or $dna[$i] eq 'G')
  {
   $counter++;
  }
}

[download]
Here the $i is incremented by three every time through the loop, which I believe is what you wanted.

-enlil

In reply to Re: for loops by Enlil
in thread Count every 3rd base occurence by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.