程嶏清单13-4.txt

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程序清单13-4：finance.pl
package Finance;
require Exporter; 
@ISA = (Exporter);
=head1 Finance.pm
Financial Calculator - Financial calculations made easy with Perl
=head 2
use Finance;
$pv = 10000.0;
$rate = 12.5 / 12; # APR per month.
$time = 360 ;      # months for loan to mature
$fv = FutureValue(); 
print $fv;
=cut
@EXPORT = qw(FutureValue, 
                       PresentValue,
                        FVofAnnuity,
                        AnnuityOfFV,
                        getLastAverage,
                        getMovingAverage,
                        SetInterest);
#
# Globals, if any
#
local $defaultInterest = 5.0;
sub Finance::SetInterest($) {
            my $rate = shift(@_);
            $defaultInterest = $rate;
            printf "\n \$defaultInterest = $rate";
}
# -------------------------------------------------------------------- 
# Notes:
# 1. The interest rate $r is given in a value of [0-100].
# 2. The $n given in the terms is the rate at which the interest
#          is applied.
#
# -------------------------------------------------------------------- 

# -------------------------------------------------------------------- 
# Present value of an investment given
# fv - a future value
# r  - rate per period
# n  - number of period
# -------------------------------------------------------------------- 
sub Finance::FutureValue($$$) {
            my ($pv,$r,$n) = @_;
            my $fv = $pv * ((1 + ($r/100)) ** $n);
            return $fv;
}
# -------------------------------------------------------------------- 
# Present value of an investment given
# fv - a future value
# r  - rate per period
# n  - number of period
# -------------------------------------------------------------------- 
sub Finance::PresentValue($$$) {
            my $pv;
            my ($fv,$r,$n) = @_;
            $pv = $fv / ((1 + ($r/100)) ** $n);
            return $pv;
}
# -------------------------------------------------------------------- 
# Get the future value of an annuity given
# mp - Monthly Payment of Annuity
# r  - rate per period
# n  - number of period
# -------------------------------------------------------------------- 
sub FVofAnnuity($$$) {
            my $fv;
            my $oneR;
            my ($mp,$r,$n) = @_;
            $oneR = ( 1 + $r) ** $n;
            $fv = $mp * ( ($oneR - 1)/ $r);
            return $fv;
}
# -------------------------------------------------------------------- 
# Get the annuity from the following bits of information
# r  - rate per period
# n  - number of period
# fv - Future Value
# -------------------------------------------------------------------- 
sub AnnuityOfFV($$$) {
            my $mp; # mp - Monthly Payment of Annuity
            my $oneR;
            my ($fv,$r,$n) = @_;
            $oneR = ( 1 + $r) ** $n;
            $mp = $fv * ( $r/ ($oneR - 1));
            return $mp;
}
# -------------------------------------------------------------------- 
# Get the average of the last "n" values in an array. 
# -------------------------------------------------------------------- 
# The last $count number of elements from the array in @values 
# The total number of elements in @values is in $number
#
sub getLastAverage($$@) {
            my ($count, $number, @values) =  @_;
            my $i;
            my $a = 0;
            return 0 if ($count == 0);
            for ($i     = 0; $i< $count; $i++) {
                        $a += $values[$number - $i - 1];
                        }
            return $a / $count;
            }
# -------------------------------------------------------------------- 
# Get a moving average of the values.
# -------------------------------------------------------------------- 
# The window size is the first parameter, the number of items in the
# passed array is next. (This can easily be calculated within the
# function using the scalar() function, but the subroutine shown here
# is also being used to illustrate how to pass pointers.) The reference to the
# array of values is passed next, followed by a reference to the place
# the return values are to be stored.
#
sub getMovingAve($$\@\@) {
            my ($count, $number, $values, $movingAve) =  @_;
            my $i;
            my $a = 0;
            my $v = 0;
            return 0 if ($count == 0);
            return -1 if ($count > $number);
            return -2 if ($count < 2);
            $$movingAve[0] = 0;
            $$movingAve[$number - 1] = 0;
            for ($i=0; $i<$count;$i++) {
                        $v = $$values[$i];
                        $a += $v / $count;
                        $$movingAve[$i] = 0;
                        }
            for ($i=$count; $i<$number;$i++) {
                        $v = $$values[$i];
                        $a += $v / $count;
                        $v = $$values[$i - $count - 1];
                        $a -= $v / $count;
                        $$movingAve[$i] = $a;
                        }
            return      0;
            }
1;
# end of Finance module