Using grep or map to solve this means that you would have to go through the entire length of the array even if the character was at the beginning. Here's a solution that stops as soon as the character is found.

sub foo {
  my ($aChars, $ch) = @_;
  my $i=0;
  for (@$aChars) {
    return $i if $ch eq $_;
    $i++;
  };
}

my @aChars =('a','b','c','d');
print "c=", findChar(\@aChars, 'c'), "\n";
# outputs c=2
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Or if you have an aversion to subs,

my $k='c';
my $i=0;

for (@aChars) { last if $k eq $_; $i++; };

print "$k=$i\n";
#also outputs c=2
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Update:Put in mssing final ';' and patched to print position=array index rather than position = ordinal value. (i.e. c=2 instead of c=3).