I know how to do it to a remote server, it would be like:
telnet www.esqsoft.globalservers.com 80
But I don't know to a local server (written in C).
Simply substitute the hostname into the url, for example for a computer on your network with the hostname "LivingRoom", use the command
telnet LivingRoom 80
.
For a server on own computer, simply use telnet localhost 80
.