Yes, many commands are accepted but the entry point is in relations; use pro/program to regenerate the parameters used / referred to in the relations.
The editor will show an error if and where your syntax is not acceptable!....(use notepad to store unfinished / unacceptable relations or the editor reverts to last acceptable listing and you could loose all the last edited lines; alternatively comment out the incorrect lines before saving)
PS there seems to be little info on what is allowable specifically.
If you find good notes specific to using c with pro-e, please post a link.
The commands are VERY LIMITED to IF / ELSE statement logic. You can not iterate to a solution based on previous computations. (e.g., no foreach or while or for x=1 .... type of syntax). PTC was experimenting with this type of capabilitiy several years ago but it never came into existance.
There are two options.
p-Shell API - Scriptable Pro/TOOLKIT that enables full control over these types of actions as an integrated application within Pro/E.
p-Program - Graphical Pro/PROGRAM editor - which enables you to better view, apply and understand pro/PROGRAM logic.