client

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

#define BUF_SIZE 1024

void err_h(char *msg);

int main(int argc,char **argv)
{
	int sock;
	char msg[BUF_SIZE];
	int str_len;
	struct sockaddr_in s_addr;

	if(argc != 3) {
		printf("Usage : %s <IP> <port>\n", argv[0]);
		exit(1);
	}

	sock = socket(PF_INET, SOCK_STREAM, 0);
	if(sock == -1)
		err_h("socket() error");

	memset(&s_addr, 0, sizeof(s_addr));
	s_addr.sin_family = AF_INET;
	s_addr.sin_addr.s_addr = inet_addr(argv[1]); 
	s_addr.sin_port = htons(atoi(argv[2]));

	if(connect(sock, (struct sockaddr *)&s_addr, sizeof(s_addr)) == -1)
		err_h("bind() error");
	else
		puts("Connected.............");

	while(1) {
		fputs("Input message(Q to quit): ", stdout);
		fgets(msg, BUF_SIZE, stdin);

		if(!strcmp(msg, "q\n") || !strcmp(msg, "Q\n"))
			break;

		write(sock, msg, strlen(msg));
		str_len = read(sock, msg, BUF_SIZE-1);
		msg[str_len] = 0;
		printf("Msg from server : %s", msg);
	}
	close(sock);

	return 0;
}

void err_h(char *msg)
{
	fputs(msg, stderr);
	fputc('\n', stderr);
	exit(1);
}

sver

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

#define BUF_SIZE 1024
#define OPSZ 4

void err_h(char *msg);
int calculate(int opnum, int opnds[], char operator);

int main(int argc,char **argv)
{
	int s_sock, c_sock;
	char opinfo[BUF_SIZE];
	int result, opnd_cnt, i;
	int recv_cnt, recv_len;

	struct sockaddr_in s_addr, c_addr;
	socklen_t c_addr_size;


	if(argc != 2) {
		printf("Usage : %s <port>\n", argv[0]);
		exit(1);
	}

	
	s_sock = socket(PF_INET, SOCK_STREAM, 0);
	if(s_sock == -1)
		err_h("socket() error");

	memset(&s_addr, 0, sizeof(s_addr));
	s_addr.sin_family = AF_INET;
	s_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	s_addr.sin_port = htons(atoi(argv[1]));

	if(bind(s_sock, (struct sockaddr *)&s_addr, sizeof(s_addr)) == -1)
		err_h("bind() error");

	if(listen(s_sock, 5) == -1)
		err_h("listen() error");

	c_addr_size = sizeof(c_addr);

	

	for(i=0; i<5; i++) {
		opnd_cnt = 0;

		c_sock = accept(s_sock, (struct sockaddr *)&c_addr, &c_addr_size);
		read(c_sock, &opnd_cnt, 1);

		recv_len = 0;
		while((opnd_cnt*OPSZ+1) > recv_len) {
			recv_cnt = read(c_sock, &opinfo[recv_len], BUF_SIZE-1);
			recv_len += recv_cnt;
		}
		result = calculate(opnd_cnt, (int*)opinfo, opinfo[recv_len-1]);
		write(c_sock, (char*)&result, sizeof(result));
		close(c_sock);
	}
	close(s_sock);
	return 0;
}

int calculate(int opnum, int opnds[], char op)
{
	int result = opnds[0], i;
	switch(op) {
		case '+':
			for(i=1; i<opnum; i++) result += opnds[i];
			break;
		case '-':
			for(i=1; i<opnum; i++) result -= opnds[i];
			break;
		case '*':
			for(i=1; i<opnum; i++) result *= opnds[i];
			break;
	}
	return result;
}



void err_h(char *msg)
{
	fputs(msg, stderr);
	fputc('\n', stderr);
	exit(1);
}