#!perl -w
use strict;
use Data::Dumper;

while (<DATA>) {
    my @tokens= m!\s*
                  (
                   \d+    # any sequence of digits
                  |[-+x/] # or an operator
                  )
                  \s*
                 !sxg;
    print Dumper \@tokens;
}

__DATA__
--1
300+400x500
3 + 4 x 5