This is not an answer to your question, but you can utilize regular expressions and the matching operation modifier e to evaluate the expression for you:

for my $input (<DATA>) {
    chomp $input;
    (my $eval = $input) =~ s/(\d+)d(\d+)(.*)/$1*(int(rand$2)+1)+$3/e;
    printf "%10s = %i\n", $input, $eval;
}

__DATA__
2d9+100
1d20+10
1d3+100
50d10-5
[download]

Good luck, and perhaps the information found here can help: Make a Text Based RPG

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)