Q. How is the second argument to AVSinput_changed() used?

Q: If I have multiple input ports (numbered 0, 1, 2, etc in C) should I specify that order number as the second argument to AVSinput_changed()?

A: No. The second argument should always be 0 for C programmers, and 1 for Fortran programmers. Internal AVS modules may accept multiple input connections (like the viewers) and this argument selects one of these connections. User modules on the other hand cannot have multiple input connections, therefore this argument should be constant.