소켓 프로그래밍에서 치명적 기호 참조 오류가 뜹니다ㅠㅠ

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
 
#define SIZE	sizeof(struct sockaddr_in)
 
main()
{
	int sockfd;
	char send_c, recv_c;
	struct sockaddr_in server = {AF_INET, 5000};
 
	server.sin_addr.s_addr = inet_addr("127.0.0.1");
 
	printf("socket()\n");
	sockfd = socket(AF_INET, SOCK_STREAM, 0);
 
	printf("connect()\n");
	connect(sockfd, (struct sockaddr *)&server, SIZE);
 
	send_c = 'A';
 
	printf("send %c to server\n", send_c);
	send(sockfd, &send_c, 1, 0);
 
	recv(sockfd, &recv_c, 1, 0);
	printf("recv %c from server\n", recv_c);
 
	printf("close()\n");
	close(sockfd);
}