This is *not* a formal assignment; it will not be collected, graded,
or reviewed.  Nevertheless, I suggest that you do it for two reasons:

*  If you can't do it, you may not have adequate background for
   the programming assignments.

*  You'll need the code for a real homework assignment...

The "assignment" is to write a network client and server.  The
client will take three command-line arguments, a host name or IP
address -- both forms must be accepted -- a port number, and a
"user name" -- make up whatever you want.  When it connects to the
server, it will first send a single line containing the user name;
it will then loop until end-of-file reading from both stdin and
the network connection.  Anything it sees on stdin, it copies to
the server; anything it sees on the network connection from the
server, it writes to stdout.

The server accepts many network connections; the only limit is the
maximum number of open file descriptors.  When a client connects,
it first reads the user name, and stores that in a per-connection
data structure.  It then reads full lines from each client.  When
it accumulates a full line from any connection, it writes that
client's user name and the line to all of the other client connections.

In other words, this is a simple, multi-client chat server.

Things to worry about include how long a line is, how to read a line
without blocking, and other forms of client misbehavior.