I have two processes (opened in a console window eachone) which cooperate, one of these processes is in waiting status, the other accept an input from a user, then send the input to the first process which elaborate. After these operations the processes exchange the roles between them, the second waits the datas from the second, which accept an input from a user and so on.
Here's the problem, if I write something in the console of the waiting process, it accepts that as input when I should insert the real input.

I need to know this, how can I do to discard the input inserted by a user to a process when it's waiting for an input from the other process and not from the user?

Sorry for my bad explanation, but I'm not so good with english

OK, let's see if I have this first part:
Program A is waiting for info from program B.
Program B is waiting for input from the user.
1) User enters information.
2) Program B sends that input to program A then waits for info from program A
3) Program A processes the info then waits for user input.
Repeat....


Here I lost you.
1) Both processes are waiting -- A for info from B, B for input from user.
2) Which process are you writing something to?
3) What is the definition of "real input" -- from the user or from the other process?


Obviously, or you wouldn't have asked... ;-)

You shouldn't have to discard input from the process that's not waiting for input -- the input should be going to the process that is waiting... Is your problem that the process waiting for user input does not have focus? If so, before waiting for input you need to use whatever command your system uses to set focus to the process.

4) Program B is waiting for info from program A.
5) Program A is waiting for input from the user.
6) User enters information.
7) Program A sends that input to program B then waits for info from program B
8 ) Program B processes the info then waits for user input.
Repeat...
Process A waits for other process input
Process B waits for user input
Now if I write something in the console of process A (i.e. the input tha I had to give to B) it will be used as input next time that A should accept an in put from user.
I have to discard the input given by keybord to a process when it's waiting for other process input.
However, I didn't thought about giving focus automatically to one or other console window, how could I do that?

I assume you know enough about system programming and documentation to find out how to find the "set focus" function for your system. After all, you found out how to "communicate between processes" and "pause a process awaiting communication" and those are part of the system documentation too...

I solved the focus problem with SetForegroundWindow, but I still have the problem with the keyboard buffer.

I don't quite understand yet. You have process A that is waiting for communication from process B.

Why is the process A window active and why are you typing into it instead of making process B the active window (SetForegroundWindow or clicking on it) so the keyboard is active in that window?

Now the active window is always the windows where I have to write the input, I want to empty the keyboard buffer in order to make the program able to manage every situation. It could happen for some reason that the wrong window is selected by the user.

What you seem to need is a way to tell if there is data in the input stream before you actually execute your input command. If there is data, read the stream and do nothing with the input.

There isn't a standard way to do this, in fact most compilers can't.

I solved with FlushConsoleInputBuffer(hInput);