Multithreaded FTP server socket VC++ - multithreading

Question

I am writing a basic FTP client server code in VC++ with multithreading.
The code works fine with single client but it doesn't work for 2 clients. I don't know how socket keep information for multiple clients.
If I do CD from on client it reflects in other one too. I mean if two different clients cannot work on different server directory.
May be something very basic I am missing here due to my lack of knowledge of socket programming.
code to accept connections:
void acceptUserConnections()
{
calen=sizeof(ca);
int thread_count = 0;
thread t[num_threads];
while(1)
{
cout<<"Accepting user connections: "<<endl;
if((cs=accept(serverSocket,&ca.generic,&calen))==INVALID_SOCKET)
throw "Couldn't accept connection\n";
string userAddress(inet_ntoa(ca.ca_in.sin_addr));
thread_count = thread_count +1;
t[thread_count] = thread(handleUserConnection, cs);
t[thread_count].detach();
//handleUserConnection(clientSocket);
}
}
}
to handle:
void handleUserConnection(SOCKET clientSocket)
{
if (strcmpi(command.c_str(),"PWD")==0)
{
ftpPWD(clientSocket);
}
}
for CD
void ftpCD(string directory, SOCKET clientSocket)
{
memset(szbuffer,'\0',1024);
if(!SetCurrentDirectory(directory.c_str()))
{
cout<<strerror(errno)<<endl;
sprintf(szbuffer,"System cannot find the specified directory.");
if(send(clientSocket,szbuffer,1024,0) == SOCKET_ERROR)
throw SEND_FAILED_MSG;
}
else
{
sprintf(szbuffer,"Directory changed successfully.");
if(send(clientSocket,szbuffer,1024,0) == SOCKET_ERROR)
throw SEND_FAILED_MSG;
}
}
for PWD
void ftpPWD(SOCKET clientSocket)
{
memset(szbuffer,'\0',1024);
int nBufferLength =GetCurrentDirectory(MAX_PATH, pwd);
if(!nBufferLength)
{
sprintf(szbuffer,"Failed to get current directory");
if(send(clientSocket,szbuffer,1024,0) == SOCKET_ERROR )
throw SEND_FAILED_MSG;
}
else
{
sprintf(szbuffer,(string(pwd)).c_str());
if(send(clientSocket,szbuffer,1024,0) == SOCKET_ERROR )
throw SEND_FAILED_MSG;
}
}
}