Re3: How to determine a variable value is a number

I don't think that passes muster.... Prove me wrong, but I believe that the expression

i_am_a_number($_) || i_am_a_number($_)
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will always be true, no matter what value you choose. You might want to rethink what $_ += 0 does for non numbers, especially ones like "12isnotanumber".

-Blake

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Re: Re3: How to determine a variable value is a number by ignatz (Vicar) on Sep 19, 2002 at 11:48 UTC
Absolutely right! Using `$_` in the sub is bad and `"15not" += 0;` becomes `15`. At the time I was just trying to understand the advice given in Far More Than Everything You've Ever Wanted to Know About... I must confess that I don't get it. Applying the advice given doesn't seem to work in all cases and so of not much use. Using Regex::Common is far and away the best solution that I have found. New version of the code that still doesn't work. #!/usr/bin/perl -w use strict; sub i_am_a_number { my $val = shift; no warnings; # += 0 on a string sets off a warning # make sure that zero is counted as a number # ($_ += 0) alone fails on zero. if ($val =~ /^\d+$/ \|\| ($val += 0)) { return 1; } return 0; } ############################################################# # take the sub on a test spin my @list = ( # Zeros 0.00, .00, 0. , 0, -0, 00, # Integers 035, 35, +19, "045 ", " 045", -2, #Floats .15, 5.5, -34.530, # Not numbers " 0 1 ", " 0 0 ", " 24 0 ", " 15hi ", "2isnotanumber", "hi!" ); for (@list) { if (i_am_a_number($_) \|\| i_am_a_number($_)) { print "$_ is a number!\n"; } else { print "$_ is not a number!\n"; } } [download] ()-() \"/ `	[reply] [d/l]

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Re: Re3: How to determine a variable value is a number
by ignatz (Vicar) on Sep 19, 2002 at 11:48 UTC

$_

"15not" += 0;

15

Far More Than Everything You've Ever Wanted to Know About...

Regex::Common

New version of the code that still doesn't work.

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

sub i_am_a_number {
    my $val = shift;
    no warnings; # += 0 on a string sets off a warning

    # make sure that zero is counted as a number
    # ($_ += 0) alone fails on zero.
    if ($val =~ /^\d+$/ || ($val += 0)) {
        return 1;
    }
    return 0;
}

#############################################################
# take the sub on a test spin

my @list = (
    # Zeros
    0.00, .00, 0. , 0, -0, 00,
    # Integers
    035, 35, +19, "045 ", " 045", -2,
    #Floats
    .15, 5.5, -34.530,
    # Not numbers
    " 0  1 ", " 0  0 ", " 24  0 ", " 15hi ", "2isnotanumber", "hi!"
);
for (@list) {
    if (i_am_a_number($_) || i_am_a_number($_)) {
        print "$_ is a number!\n";
    } else {
        print "$_ is not a number!\n";
    }
}
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()-()
 \"/
  `

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