if ($array[0] =~ /^\d+$/) {
    # do something
}

##</code><code>##

sub is_whole_number { $_[0] =~ /^\d+$/            }
sub is_integer      { $_[0] =~ /^[+-]?\d+$/       }
sub is_float        { $_[0] =~ /^[+-]?\d+\.?\d*$/ }