General :: Make Change In Tcp.cc Over NS-2.34?

I have problem when I add another case in linear increase cogestion avoidance algorithm in tcp.cc why can't it work out when I run it?In the tcl code I have set windowOption_ to '9' (where I put my additional change).It seems that any change I've made doesn't take effect at all.What am I suppose to do to make it work? I make change like this :

void TcpAgent:pencwnd()
{
double increment;
if (cwnd_ < ssthresh_) {
/* slow-start (exponential) */
cwnd_ += 1;
code....