in reply to Chomp Maybe?

A couple points:

When using DBI and prepare, use placeholders. If you don't know what they are, read the doc. To put it simply, you can put a ? in the prepare statement, pass values for each in the execute, and it will properly quote it for you. In your case, something like this 

my $dbh = $db->prepare("SELECT balance FROM Table1 WHERE username=? an
+d balance < '-.01'");
$dbh->execute($authuser);
my ($balance_due) = $dbh->fetchrow_array;

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would work. This is good for untrusted data.

Anyway, the easiest solution to your problem would be to simply negate the value, which would yield a positive. So something like 

$balance_due = -$balance_due

# or

$balance_due = $balance_due * -1;

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would be good and result in $balance_due being equal to 9.99.

To answer your question using a different way, you could also use a substitution regex 

$balance_due =~ s/-//;

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to strip out (literally replace it with nothing) the first - it finds. If you don't understand what it going on, read up on perlretut.

Added Second paragraph.

Replies are listed 'Best First'.
Re: Re: Chomp Maybe?
by hardburn (Abbot) on Jul 01, 2003 at 18:24 UTC

    Actually, I think it would be better to just get the absolute value:

    $balance_due = abs($balance_due);

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    This protects you in the event that $balance_due is a positive number (which shouldn't happen according to the SQL, but I've always beleived that a good programmer is someone who looks both ways on a one way street). It's also close enough in speed to negation that random noise is a factor in execution time. Code:

    #!/usr/bin/perl
use strict;
use warnings;
use Benchmark qw(cmpthese);

my $data  = -12345;
my $count = pop || 500000;

cmpthese($count, {
    negate   => sub { my $i = -$data }, 
    absolute => sub { my $i = abs($data) }, 
    regex    => sub { my ($i) = $data =~ s/-// }, 
});

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    Results:

    Benchmark: timing 500000 iterations of absolute, negate, regex...
  absolute:  1 wallclock secs ( 1.24 usr +  0.00 sys =  1.24 CPU) @ 40
+4858.30/s (n=500000)
    negate:  1 wallclock secs ( 1.15 usr +  0.00 sys =  1.15 CPU) @ 43
+3275.56/s (n=500000)
     regex:  3 wallclock secs ( 3.16 usr +  0.00 sys =  3.16 CPU) @ 15
+8328.06/s (n=500000)
             Rate    regex absolute   negate
regex    158328/s       --     -61%     -63%
absolute 404858/s     156%       --      -7%
negate   433276/s     174%       7%       --

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    ----
    I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
    -- Schemer

    Note: All code is untested, unless otherwise stated

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[d/l]
[select]
      ++, you're absolutely right. When writing up my node, I forgot all about just getting the absolute value. ; )
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Re: Re: Chomp Maybe?
by th3monk3y (Novice) on Jul 01, 2003 at 04:52 UTC
    Works like a charm! You guys are awesome! Thanks for your prompt reply! Regards, -Paul
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