간단한 소켓프로그램인데요, 소켓 연결은 되는데 값이 저장이 안되는 것 같아요ㅠㅠ

cal_data라는 구조체를 만들어서 연산자와 피연산자를 넘겨주는건데요....
소켓 연결까지는 되는데, 리눅스에서 실행해보면(./프로그램명 연산자 피연산자 연산기호)
서버에서 계산한 답이 나와야 하는데 그냥 %d %c %d = %d 이렇게 문자가 뜹니다ㅋㅋㅠㅠㅠㅠㅠ

소켓프로그래밍을 이제 막 공부하는 중이라 잘못된 부분이 어디인지를 봐도 잘 모르겠어요ㅠㅠ
어디가 잘못된건가요?ㅠㅠㅠㅠㅠ

////////////////client-리눅스//////////////////

struct cal_data
{
int left_num;
int right_num;
char op;
int result;
short int error;
};

int main(int argc, char **argv)
{
struct sockaddr_in server_addr;
struct cal_data rdata;
int server_sockfd;
char buffer[256];
int len;
int left_num, right_num;

if(argc != 4)
{
perror("Usage : %s [num1] [num2] [0p]\n", argv[0]);
return 1;
}

rdata.left_num = atoi(argv[1]);
rdata.right_num = atoi(argv[2]);
rdata.op = argv[3][0];

server_sockfd = socket(AF_INET, SOCK_STREAM, 0);

if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0) == -1))
{
perror("error :");
return 1;
}

memset((void *)&server_addr, 0x00, sizeof(server_addr));

server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(PORT);
server_addr.sin_addr.s_addr = inet_addr(IP);

if(connect(server_sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1)
{
perror("connnect error :");
return 1;
}

rdata.left_num = htonl(rdata.left_num);
rdata.right_num = htonl(rdata.right_num);

read(server_sockfd, (void *)&rdata, sizeof(rdata));
rdata.error = 0;

write(server_sockfd, (void *)&rdata, sizeof(rdata));
rdata.error = 0;

if(ntohs(rdata.error != 0))
{
perror("CALC error %d\n", ntohs(rdata.error));
}
perror("%d %c %d = %d\n", ntohl(rdata.left_num), rdata.op, ntohl(rdata.right_num), ntohl(rdata.result));

close(server_sockfd);
return 0;
}

/////////////////////////server-윈도우/////////////////////////////
struct cal_data
{
int left_num;
int right_num;
char op;
int result;
short int error;
};

int main(int argc, char **argv)
{
WSADATA WSAData;
sockaddr_in client_addr, sock_addr;
SOCKET listen_s, client_s;
int len, addr_len;
struct cal_data sdata;
int left_num, right_num;
short int cal_result;
int recvn, sendn;

if(WSAStartup (MAKEWORD (2,2), &WSAData) != 0)
{
return 1;
}

listen_s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if(listen_s == INVALID_SOCKET)
{
return 1;
}

ZeroMemory((void *)&sock_addr, sizeof(sock_addr));
sock_addr.sin_family = AF_INET;
sock_addr.sin_addr.s_addr = htonl(INADDR_ANY);
sock_addr.sin_port = htons(PORT);

if(bind(listen_s, (struct sockaddr *)&sock_addr, sizeof(sock_addr)) == -1)
{
printf("Error ");
return 1;
}

if(listen(listen_s, 5) == -1)
{
printf("Error ");
return 1;
}

for(;;)
{
addr_len = sizeof(client_addr);
client_s = accept(listen_s, (struct sockaddr *)&client_addr, &addr_len);

if(client_s == -1)
{
printf("Error ");
return 1;
}

len = sizeof(sdata);

recvn = recv(client_s, (char *)&sdata, len, 0);
if(recvn != len)
{
return 1;
}

sdata.error = 0;
left_num = ntohs(sdata.left_num);
right_num = ntohs(sdata.right_num);

switch(sdata.op)
{
case '+':
cal_result = left_num + right_num;
break;
case '-':
cal_result = left_num - right_num;
break;
case '*':
cal_result = left_num * right_num;
break;
case '/':
if(right_num == 0)
{
sdata.error = 2;
break;
}
cal_result = left_num / right_num;
break;
default:
sdata.error = 1;
}

sdata.result = htonl(cal_result);
sdata.error = htons(cal_result);

sendn = send(client_s, (char *)&sdata, len, 0);
if(sendn != len)
{
return 1;
}
closesocket(client_s);
}

closesocket(listen_s);
WSACleanup();
return 0;

}