How to compare the package version?

[hhding <hhding.gnu@gmail.com>]

hi list

Assume I have installed gcc-4.1 with version 4.1.2-15, and some 
application need gcc with version greater than 4.1.2-18. How can I check 
and compare the installed gcc version in debian way then decide install 
the new version or not? I have read the debian policy manual, but no 
version compare tool or command is mentioned.

hhding