how to get thread ID in visual C#

Call to get the current managed thread id.

int threadId = System.Threading.Thread.CurrentThread.ManagedThreadId;

If you what the current process id where all your threads lives.

int processId = System.Diagnostics.GetCurrentProcess().Id;

You've already been answered. But here's some info that may not be obvious. ManagedThreadId returns the unique ID associated with the managed thread. This is not the ID of the underlying native thread. So you cannot pass this to any native API that requires a threadId parameter.

For that you need to P/Invoke GetCurrentThreadId from the running thread. Beware though. It's risky to cache this value because under certain circumstances the CLR may move a managed thread into a different native thread (it's extremely rare, but is not an impossible scenario). So you need to call this prior to using it so you know you can use it safely. If you use it within the same method, the CLR cannot move the managed thread for the duration of that method call.

Another hack people use is to intentionally introduce a native stack frame into the call stack. This will prevent the CLR from moving the managed thread into a new native thread since that will completely wreck the call stack. I can't see any really good reasons to resort to such extreme measures though.