Polish notation(s) converter using Flex/Bison

Example input file:

* 3 + 4 5 -> in
25 / 5 + 3 + 4 / 2 -> post

will output:

3 * (4 + 5) = 27
25 5 / 3 + 4 2 / + = 10

On the first line, the program takes an expression in prefix (Polish) notation and outputs it in infix (Common, parenthesized) notation. The second line was converted from infix notation to postfix (Reverse polish) notation.