how to combine two modules into one?

hi guys

i'm trying to combine two modules into one main module.

that will connect both of them and create signals to go to one of them

(like c in module 2 in the example)

in the first the inputs and outputs should be connected to the second module, and the same in the second module in which has inputs not from the first one.

for example:

module 1:

input a;//from module 2

output b;//to module 2

module 2

input b;//from module 1

output a;//to module 1

input c;

i tried to do it in different ways but i get errors all the time..

what's the right way or syntax to do it?

thanx