Manipulating the tree Structure

[Andrea Callia D'Iddio]

Hi all,
first of all i want to thank you for the aid that i have receveid from
this mailing list. I have another little question:
if i have a statemente that is an expression, for example x+5 , how
can i know if the operation is plus (+), or minus (-), or equal(=) or
less (<) etc..
Can you give me the name of the file containing all these definition??
Thanks to all,
Andrea