help me to understand this UDP source code

[RyuKnightly]

hello i'm learning about UDP .and i learn from this source.
i get a little problem . it's error for compiling .
anyone would help me to correct this source ?

#include <windows.h>
#include <winsock.h>
#include <stdio.h>
#include <conio.h>


//automatically link with winsock
#pragma comment(lib, "wsock32.lib")



// Address definitions to be used in the multicast() function
#define MULTICAST_GROUP_IP		"234.5.6.7"
#define DEFAULT_PORT			15
#define DEFAULT_TTL				7
#define STRING_LENGTH			100



// Bread&butter error reporting
void PrintWinsockError()
{
	LPVOID lpMsgBuf;
	
	int iError = WSAGetLastError();
	
	if(FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, 0, iError, 0, (LPTSTR)&lpMsgBuf, 0, 0))
	{
		cprintf("WSAGetLastError %d: %s", iError, lpMsgBuf);
		LocalFree(lpMsgBuf);
	}
	else
	{
		cprintf("WSAGetLastError %d", iError);
	}
}



// Address-to-ip resolution
int iResolve(SOCKADDR_IN &addrResolve, char *cHost, UINT uiPort, UINT uiInterface)
{
	struct in_addr iaHost; // Used to resolve IP and connect
	LPHOSTENT lpHost; // Used to connect
	unsigned int iIndex;

	iaHost.s_addr = inet_addr((LPCSTR)cHost); // Check if this syntax is consistent with IP address

	if(iaHost.s_addr == INADDR_NONE) // If not IP, must be hostname string
	{
		lpHost = gethostbyname(cHost); // Get host structure by host name
		if(lpHost == NULL)return false; // Whoops! Unresolved hostname!
	}
	else // This is an IP so just get structure by address
	{
		lpHost = gethostbyaddr((LPCSTR)&iaHost, sizeof(struct in_addr), AF_INET); // Get host structure by address
		if(lpHost == NULL)return false; // Whoops! Unresolved host IP!
	}

	for(iIndex = 0; iIndex < uiInterface; iIndex++)
		if(!lpHost->h_addr_list[iIndex])
			return false;
	if(!lpHost->h_addr_list[uiInterface])
		return false;

	memset(&addrResolve, NULL, sizeof(addrResolve));
	addrResolve.sin_family = AF_INET; // We only use internet addresses
	addrResolve.sin_addr = *((LPIN_ADDR)lpHost->h_addr_list[uiInterface]); // The remote IP
	addrResolve.sin_port = htons(uiPort); // The remote port

	// Okays
	return true;
}



// Work out which ip comes first on this machine, or nth ip if iInterface is specified
bool bGetNetworkInterface(IN_ADDR &in_addrLocal, unsigned int uiInterface = 0)
{
	char cLocalHostName[MAX_PATH];

	gethostname(cLocalHostName, sizeof(cLocalHostName));
	SOCKADDR_IN addrLocal;
	
	if(!iResolve(addrLocal, cLocalHostName, 0, uiInterface))
		return false;

	in_addrLocal = addrLocal.sin_addr;

	return true;
}



// Function to associate a socket with a multicast group
bool bJoinMulticastGroup(SOCKET UDP_Socket, char *cMulticastGroup)
{
	// Used to set multicast TTL
	char cTTL = DEFAULT_TTL;

	// Set the multicast ttl
	int iRet = setsockopt(UDP_Socket, IPPROTO_IP, IP_MULTICAST_TTL, (char *)&cTTL, sizeof(cTTL));

	if(iRet == SOCKET_ERROR)
	{
		cprintf("Failed to set multicast ttl\r\n");
		PrintWinsockError();
		return false;
	}

	// Add socket to be a member of the multicast group
	struct ip_mreq	ipmr;
	ipmr.imr_multiaddr.s_addr = inet_addr(cMulticastGroup);
	bGetNetworkInterface(ipmr.imr_interface); // Does the job of... ipmr.imr_interface.s_addr = inet_addr("ip");
	iRet = setsockopt(UDP_Socket, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&ipmr, sizeof(ipmr));
	
	if(iRet == SOCKET_ERROR)
	{
		cprintf("Failed to add multicast membership\r\n");
		PrintWinsockError();
		return false;
	}

	// Set the local interface from which multicast is to be transmitted
	IN_ADDR inLocal;
	bGetNetworkInterface(inLocal); // Does the job of inLocal = inet_addr("ip");
	setsockopt(UDP_Socket, IPPROTO_IP, IP_MULTICAST_IF, (char *)&inLocal, sizeof(inLocal));
	
	if(iRet == SOCKET_ERROR)
	{
		cprintf("Failed to set multicast interface\r\n");
		PrintWinsockError();
		return false;
	}

	return true;
}


// Function that receives UDP packets (not just multicast ones)
bool bReceiveMulticast(SOCKET UDP_Socket, char *cMulticastGroup)
{
	// Used to identify where the packet came from
	SOCKADDR_IN		addrFrom;

	// String to hold the packet data
	char cData[STRING_LENGTH];

	// Holds status of incoming packet queue
	ULONG ulQueue[1];

	// Tracks if any packets are received
	bool bGotPacket = false;

	while(true)
	{
		// Did a packet come through?
		*ulQueue = NULL; // Reset incoming packet status
		if(ioctlsocket(UDP_Socket, FIONREAD, (ULONG FAR *)ulQueue)) // Ask the socket how many packets are waiting
		{
			cprintf("ioctlsocket failed\r\n");
			PrintWinsockError();
			return false;
		}

		// No packets waiting?
		if(!*ulQueue)
			break;

		// Receive the packet
		int size = sizeof(addrFrom);
		int iRet = recvfrom(UDP_Socket, (char *)cData, sizeof(cData) - 1, 0, (struct sockaddr*)&addrFrom, &size);
		if(iRet == SOCKET_ERROR)
		{
			cprintf("Packet arrived, but failed to be received\r\n");
			PrintWinsockError();
			return false;
		}

		// Terminate packet so we can display it as a string
		cData[iRet] = 0;

		// Print the contents of the packet
		cprintf("Received packet from %s: \"%s\"\r\n", inet_ntoa(addrFrom.sin_addr), cData);

		bGotPacket = true;
	}

	// If no packets received, inform the user
	if(!bGotPacket)
		cprintf("No packets received\r\n");

	return true;
}

// Function that sends a multicast
bool bSendMulticast(SOCKET UDP_Socket, char *cMulticastGroup)
{
	// Used to track return values of functions
	int				iRet;

	// Where the packet will be heading
	SOCKADDR_IN		addrDest;
	memset(&addrDest, 0, sizeof(addrDest));

	// String to hold the packet data
	char cData[STRING_LENGTH];

	// Destination IP Address
	addrDest.sin_family			= AF_INET;
	addrDest.sin_port			= htons(DEFAULT_PORT);
	addrDest.sin_addr.s_addr	= inet_addr(cMulticastGroup);

	// Data to send
	memset(cData, 0, sizeof(cData));
	wsprintf((char *)cData, "Hello World!");

	// Send to MULTICAST
	iRet = sendto(UDP_Socket, (char *)cData, (int)strlen(cData), 0, (struct sockaddr*)&addrDest, sizeof(addrDest));
	if(iRet == SOCKET_ERROR)
	{
		cprintf("Packet failed to be sent\r\n");
		PrintWinsockError();
		return false;
	}

	
	return true;
}


// Application entry point
int main(int argc, char *argv[], char *envp[])
{
	// Local for return value checking
	int iRet;

	// Used for winsock startup
	WORD			wVersionRequested;
	WSADATA			wsaData;

	// Initialise winsock, latest version
	wVersionRequested = MAKEWORD(2, 2);
	iRet = WSAStartup(wVersionRequested, &wsaData);
	if(iRet != 0)
	{
		WSACleanup();
		cprintf("Failed to start winsock\r\n");
		return false;
	}

	// Create a new socket
	SOCKET UDP_Socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if(UDP_Socket==INVALID_SOCKET)
	{
		cprintf("Failed to create socket\r\n");
		PrintWinsockError();
		return false;
	}

	// Bind socket to port
	SOCKADDR_IN addrLocal;
	addrLocal.sin_family		= AF_INET;
	addrLocal.sin_port			= htons(DEFAULT_PORT);
	bGetNetworkInterface(addrLocal.sin_addr); // Same as... addrLocal.sin_addr.s_addr = inet_addr("yourip");
	iRet = bind(UDP_Socket, (LPSOCKADDR)&addrLocal, sizeof(struct sockaddr));
	if(iRet == SOCKET_ERROR)
	{
		cprintf("Failed to bind socket\r\n");
		PrintWinsockError();
		return false;
	}

	cprintf("Using UDP port %d, press any key to exit\r\n", DEFAULT_PORT);
	cprintf("Attempting to join multicast group %s... ", MULTICAST_GROUP_IP);

	// Join multicasting group
	if(bJoinMulticastGroup(UDP_Socket, MULTICAST_GROUP_IP))
		cprintf("done\r\n\r\n");
	else
		cprintf("FAILED\r\n");

	while(true)
	{
		// Send a multicast packet
		if(bSendMulticast(UDP_Socket, MULTICAST_GROUP_IP))
			cprintf("Multicast sent to group %s\r\n", MULTICAST_GROUP_IP);

		// Wait for echo packet to arrive, just in case the network is laggy
		Sleep(100);

		// Receive a packet
		bReceiveMulticast(UDP_Socket, MULTICAST_GROUP_IP);

		// Dont overwhelm the user
		Sleep(1000);
		if(kbhit())break;
		Sleep(1000);
		if(kbhit())break;
		Sleep(1000);
		if(kbhit())break;
	}

	// Close socket, kill winsock
	closesocket(UDP_Socket);
	WSACleanup();

	// Quit
	return iRet;
}

i got source code from this website

http://www.gamedev.net/page/resources/_/technical/multiplayer-and-network-programming/advanced-winsock-multiplayer-game-programming-r1587?


please advice to learn UDP.
what's the best ebook for beginer networking(UDP) .
thanks you.
sorry for my bad english