use strict;
my @data;
my $avg;
my $dev;
my $std;
my $tmp;
my $grade;
my $line;

open(IN, "pa5c.dat") || die ("Can't open file $!\n");
while($line = <IN>){
  		chomp ($line);
 		my $tmp = [split /:/];
  		$avg += $tmp->[1];
  		push @data, $tmp;

}
$avg = scalar(@data) ? $avg /= @data : 0;


my $std = 0;
for (@data) { $std += abs($_->[1] - $avg) }
		$std = scalar(@data) ? $std /= @data : 0;

open(OUT, ">pa5c.dat") || die ("Can't open file $!\n");
		for (@data) {
  		my $grade;
  		my $dev = ($_->[1] - $avg) / $std;
  		if ($dev >= 1) { $grade = 'A' }
  		elsif ($dev >= (1/3)) { $grade = 'B' }
 		elsif ($dev >= (-1/3)) { $grade = 'C' }
 		elsif ($dev > -1) { $grade = 'D' }
 		else { $grade = 'E' }
 		print OUT join (':', $_->[0], $_->[1], $grade) . "\n";
}

close OUT;


__END__#pa52.pl
##</code><code>##

Smith:70
Jones:74
Rider:80
High:82
Billie:68
Smithsonville:76