network

I have a question: In GAMS, is there something similar to "structure" in C ?
I need to define a network optimization problem and I need to define: A node as the structure, incoming arcs as one attribute, and outgoing arcs as another attribute.

GAMS does not have that and most likely you don’t “need” that anyway. A compact way to describe a network is shown here:

http://yetanothermathprogrammingconsultant.blogspot.com/2011/06/network-formulation.html

Some small improvements over this formulation for even larger problems are documented here: http://yetanothermathprogrammingconsultant.blogspot.com/2011/08/more-on-network-models.html.