this code:

--snip--
@lcase = (a..z);
@other = ();
for ($i = 0; $i <= $#lcase; $i++) {
 if ($i % 2) {
  @other[$i] = uc($lcase[$i]);
 }
 else {
  @other[$i] = $lcase[$i];
 }
}

print "lcase:";
foreach $l (@lcase) { print " $l"; }
print "\n";

print "other: ";
foreach $o (@other) { print " $o"; }
print "\n";
--snip--
[download]

gives these results:

$ perl asdsda.txt
lcase: a b c d e f g h i j k l m n o p q r s t u v w x y z
other: a B c D e F g H i J k L m N o P q R s T u V w X y Z

hope that helps.