perl -le 'for (qw/0 1 19 32.4 100 77 138 342.1/) { print "$_ is ", /^(?:100|\d\d?)$/ ? "valid input" : "invalid input"}'

##</code><code>##

0 is valid input
1 is valid input
19 is valid input
32.4 is invalid input
100 is valid input
77 is valid input
138 is invalid input
342.1 is invalid input