socket Server Select programming

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

void error(const char *msg)
{
perror(msg);
exit(1);
}

int main(int argc, char *argv[])
{
if(argc < 2){
fprintf(stderr, "Port No not provided. Program terminated\n");
exit(1);
}


int sockfd, newsockfd, portno, n;
char buffer[255];

struct sockaddr_in serv_addr, cli_addr;
socklen_t clilen;

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0)
{
error("Error opening Socket.");
}

bzero((char *) &serv_addr, sizeof(serv_addr));
portno = atoi(argv[1]);

serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);

if(bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
error("Binding Failed.");

listen(sockfd, 5);
clilen = sizeof(cli_addr);

newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);

if(newsockfd < 0)
error("Error on Accpt");

int num1, num2, ans, choice;

S : n = write(newsockfd, "Enter Number 1 : ", strlen("Enter Number 1")); // Ask for Number 1
if (n < 0)
error("Error writing to socket");
read(newsockfd, &num1, sizeof(int)); // Read No1
printf("client - Number 1 is : %d\n", num1);

n = write(newsockfd, "Enter Number 2: ", strlen("Enter Number 2"));  // Ask for Number 2
if (n < 0)
error("Error writing to socket");
read(newsockfd, &num2, sizeof(int)); //Read No2
printf("client - Number 2 is : %d\n", num2);

n = write(newsockfd, "Enter your choice : \n1.Addition\n2.Subtraction\n3.Multiplication\n4.Division\n5.Exit\n", strlen("Enter your choice : \n1.Addition\n2.Subtraction\n3.Multiplication\n4.Division\n5.Exit\n")); // Ask Choice
if (n < 0)
error("Error writing to socket");
read(newsockfd, &choice, sizeof(int)); //Read choice
printf("client - Choice is : %d\n", choice);

switch(choice){
case 1:
ans = num1 + num2;
break;
case 2:
ans = num1 -num2;
break;
case 3:
ans = num1*num2;
break;
case 4:
ans = num1/num2;
break;
case 5:
goto Q;
break;
}

write(newsockfd, &ans, sizeof(int));
if(choice !=5)
goto S;

Q: close(newsockfd);
close(sockfd);
return 0;

}

// compile gcc -o server server.c

// server 9999