How to convert float to Real_Integer ?

If there was a function that allows to convert any type (double float, integer) to real_integer That would be great to post its name and the class it belongs to . I created a dialog box where i pick values in order to create BRepPrimAPI_MakeBox, but i just can't do it because of the conversion pb. Indeed, the BRepPrimAPI_MakeBox takes only real_integer as arguments. It displays nothing on the screen. Thank you for you help. Omar Msaaf