All i need is a client and a server on TCP with concurrency. (i mean the use of fork()). The server will listed on an ip+port. The client will connect to the server and send some info to the server. mostly all of them are text. and finally the server will accept them and save them in a file. Now i need help... specially i have a code segment of a echo server, but i need a piece of code as a help as atleast sending a string. If i can send a string from server to client and vice versa, i can do the rest... please help me...

i have no time and my lots of grade depends on it.... help me guys...

Always the place to start... (http://beej.us/guide/net/)

Did they give you an assignment without teaching you the concepts behind it? That site from brazilnut seems decent, but always make sure to read the manpages/infopages (specifically info libc) so that you actually learn what to do in situations other than those in the tutorial.
ta0kira

Ask your TA. That's what they're there for. Also, until I read the word "grade", I was thinking about suggesting using socat, or, if you really wanted to code something yourself, using SDL for sockets (it's dead simple and portable) and concurrency (threads are not that bad either). But as this is homework, there's likely requirements you haven't told us about...

That, and a grade is given for a reason...
ta0kira