You will get these warnings because some compilers are more strict about type conversions. MSVC++ 5.0+ is one of these. The two common types of assignments that cause these warnings (in large quantity) can be safely ignored:
In lex output code: Assigning the value ~0U to a unsigned variable.
In yacc output code: Assigning values between 32k and 64k to a short int.
To suppress these warnings with MSVC++ 5.0 add this line to the start of your Lex and Yacc output code:
#pragma warning( disable : 4305 )
Note:
This issue was fixed in the 3.3 release of MKS Lex & Yacc. | 
