op_client.c

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

#define BUF_SIZE    1024
#define OPSZ        4

int main(int argc, char **argv) 
{
    int sock;
    char opmsg[BUF_SIZE];
    int result, opnd_cnt;
    struct sockaddr_in serv_addr;

    if(argc != 3) {
        printf("usage : %s <IP> <PORT>\n", argv[0]);
        return -1;
    }

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if(sock < 0) {
        perror("socket");
        return -1;
    }

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

    if(connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("connect");
        close(sock);
        return -1;
    }

    printf("Operand Count : ");
    scanf("%d", &opnd_cnt);
    opmsg[0] = (char)opnd_cnt;

    for(int i=0; i<opnd_cnt; i++) {
        scanf("%d", (int *)&opmsg[1+OPSZ*i]);
    }

    printf("Operator : ");
    scanf(" %c", &opmsg[opnd_cnt*OPSZ+1]);
    write(sock, opmsg, opnd_cnt*OPSZ+2);
    read(sock, &result, sizeof(int));
    
    printf("Operand result : %d\n", result);
    close(sock);
    return 0;
}

op_server.c

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

#define BUF_SIZE    1024
#define OPSZ        4

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

int main(int argc, char **argv) 
{
    int sock, clnt_sock;
    struct sockaddr_in sock_addr, clnt_addr;
    socklen_t clnt_size;
    char opinfo[BUF_SIZE];
    int recv_cnt, recv_len;
    int opnd_cnt, result;

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if(sock < 0) {
        perror("sock");
        return -1;
    }
    
    memset(&sock_addr, 0, sizeof(sock_addr));
    sock_addr.sin_family = AF_INET;
    sock_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    sock_addr.sin_port = htons(atoi(argv[1]));

    if(bind(sock, (struct sockaddr *)&sock_addr, sizeof(sock_addr)) < 0) {
        perror("bind");
        close(sock);
        return -1;
    }

    if(listen(sock, 5) < 0) {
        perror("listen");
        close(sock);
        return -1;
    }

    clnt_size = sizeof(clnt_addr);
    for(int i=0; i<5; i++) {
        clnt_sock = accept(sock, (struct sockaddr *)&clnt_addr, &clnt_size);
        if(clnt_sock < 0) {
            perror("accept");
            close(sock);
            return -1;
        }
        read(clnt_sock, &opnd_cnt, 1);
        recv_len = 0;
        while(recv_len < opnd_cnt*OPSZ +1) {
            recv_cnt = read(clnt_sock, &opinfo[recv_len], BUF_SIZE - 1);
            if(recv_cnt < 0) {
                perror("read");
                close(sock);
                close(clnt_sock);
                return -1;
            }
            recv_len += recv_cnt;
        }
        
        result = calculate(opnd_cnt, (int*)opinfo, opinfo[recv_len -1]);
        write(clnt_sock, &result, sizeof(result));
        close(clnt_sock);      
    }
    close(clnt_sock);
    return 0;
}