#!/usr/bin/perl
use strict;
use warnings;

my @numbers = qw(1 -1 123.1 0.1 Characters);

foreach my $number (@numbers) {
    if ($number =~ /^[+-]?\d+\z/ ) { 
	print "The $number is a +/- integer\n"; 
    }
    elsif ($number =~ /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) { 
	print "The $number is a C float\n"; 
    }
    elsif ($number =~ /\D/ ) { 
	print "The $number has nondigits\n";
    }
}

__END__

The 1 is a +/- integer
The -1 is a +/- integer
The 123.1 is a C float
The 0.1 is a C float
The Characters has nondigits