少し長いので2つにわけます。

#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define RCVBUFSIZE 32

void DieWithError(char *errorMessage);

int main(int argc, char *argv[]){

int sock;
struct sockaddr_in echoServAddr;
unsigned short echoServPort;
char *servIP;
char *echoString;
char echoBuffer[RCVBUFSIZE];
unsigned int echoStringLen;
int bytesRcvd, totalBytesRcvd;

if((argc < 3) || (argc > 4)){
fprintf(stderr, "Usage: %s <server IP> <Echo Word> [<Echo Port>]n", argv[0]);
exit(1);
}