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

    use constant EXPENSE_FILE      => 'expense.dat';
    use constant EXPENSE_REPORT    => 'final_expense.txt';
    use constant FIELDS_PER_RECORD => 4;
    use constant REPORT_HEADER     => "Department,Total\n";

    open IN_FILE, "<", EXPENSE_FILE
        or die "Cannot open ".EXPENSE_FILE." for reading: $!";
    my @expenses = <IN_FILE>;
    close IN_FILE;

    my %deptTotals;

    foreach my $expense ( @expenses ) {
        my %record;
        my @fields = qw/ dept empID amount desc /;
        @record{ @fields } = split /,/, $expense, FIELDS_PER_RECORD;
        if ( ! exists $deptTotals{ $record{ dept } } ) {
            $deptTotals{ $record{ dept } } = 0;
        }
        $deptTotals{ $record{ dept } } += $record{ amount };
    }

    open OUT_FILE, ">", EXPENSE_REPORT
        or die "Cannot open ".EXPENSE_REPORT." for writing: $!";

    print OUT_FILE REPORT_HEADER;
    foreach my $dept ( sort keys %deptTotals ) {
        print OUT_FILE "$dept,$deptTotals{ $dept }\n";
    }
    close OUT_FILE;