C lang，多客户端服务器，错误:非Socket操作

I've got an assignment to write a server program that accepts multiple clients. I'm writing in C language and trying to accomplish this using a select() statement. I am able to compile, but whenever I telnet in, I get a "Socket operation on non-socket error." I've tried researching the error, but can't find anything too helpful. Any assistance would be appreciated.I've got an assignment to write a server progra