Is there a boost library that allows you to specify the range that a number can take, e.g. boost::range< int, 1, 12 > month; generating an error on an invalid range, e.g. month = 20; // [1] oops! Also, is it possible to distinguish between a number literal like the above and a variable assignment, like: month = m; // [2] The logic behind this is to provide compile-time checks where possible, so [1] would produce a compile-time error and [2] would be a run-time error. You could also do something like: inline char & string::operator[]( boost::range< int, 5, 10 > i ){ ... } // ... string s; s[ 1 ] = 'a'; // oops! and class date { boost::range< int, 1, 12 > month; public: inline date( boost::range< int, 1, 12 > m ): month( m ){} }; Regards, Reece _________________________________________________________________ Sign-up for a FREE BT Broadband connection today! http://www.msn.co.uk/specials/btbroadband