#!/lusr/bin/perl -w
use strict;

my $total_length = 0;
my %charCount = ();


#open_file();
#process_file();
#compute_value();
#print_total();



sub open_file {
    print "Enter filename:  ";
    my $filename = <STDIN>;
    open (SEQUENCE, $filename) or die "Can't open the DNA sequence file: $filename\n";
}

sub process_file {
    while (<SEQUENCE>){
	chomp($_);
	my $length = length($_);
	for (my $i = 0; $i < $length; $i++){
	    my $char = substr($_, $i, 1);
	    $charCount{$char}++;
	}
	$total_length += $length;
    }
    close(SEQUENCE);
}

sub compute_value {
    foreach my $char (keys %charCount){
	my $fraction = 100 * $charCount{$char} / $total_length;
	print "The character $char occurs $charCount{$char} times, or $fraction %\n";
    }
}

sub print_total {
    print "Total length is $total_length.\n";
}

open_file();
process_file();
compute_value();
print_total();