Hello, I'm currently working on an assignment that requires C but I only have experience with C++ so I'm having some trouble.
The assignment is asking me to implement a client/server that communicates with each other over UDP. Basically the client is supposed to send over a number as a command line input(up to 128 characters) and the server needs to check if it is indeed a number. If it is, then it adds up the individual digits until there is only one digit and then sends the result to the client.
Example
Enter string: 123456789101234567891012345678910
From server: 138
From server: 12
From server: 3
Here is what I have so far:
Server
ClientCode:/* Creates a datagram server. The port number is passed as an argument. This
server runs forever */
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
#include <stdio.h>
#include <ctype.h>
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int sock, length, n;
socklen_t fromlen;
struct sockaddr_in server;
struct sockaddr_in from;
char buf[1024];
int sum = 0;
if (argc < 2) {
fprintf(stderr, "ERROR, no port provided\n");
exit(0);
}
sock=socket(AF_INET, SOCK_DGRAM, 0);
if (sock < 0) error("Opening socket");
length = sizeof(server);
bzero(&server,length);
server.sin_family=AF_INET;
server.sin_addr.s_addr=INADDR_ANY;
server.sin_port=htons(atoi(argv[1]));
if (bind(sock,(struct sockaddr *)&server,length)<0)
error("binding");
fromlen = sizeof(struct sockaddr_in);
while (1) {
n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
if (n < 0) error("recvfrom");
write(1,"Received a datagram: ",21);
write(1,buf,n);
for(int i = 0; i < strlen(buf); i++){
if(!isdigit(buf[i])){
n = sendto(sock,"We can't compute!\n",19,0,(struct sockaddr *)&from,fromlen);
}
}
n = sendto(sock,"We can compute!\n",17,0,(struct sockaddr *)&from,fromlen);
snprintf(buf, sizeof(buf), "%c", sum);
n = sendto(sock,buf,128,0,(struct sockaddr *)&from,fromlen);
if (n < 0) error("sendto");
}
return 0;
}
The part I'm stuck on is this part from the server codeCode:/* UDP client in the internet domain */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
void error(const char *);
int main(int argc, char *argv[])
{
int sock, n;
unsigned int length;
struct sockaddr_in server, from;
struct hostent *hp;
char buffer[256];
if (argc != 3) { printf("Usage: server port\n");
exit(1);
}
sock= socket(AF_INET, SOCK_DGRAM, 0);
if (sock < 0) error("socket");
server.sin_family = AF_INET;
hp = gethostbyname(argv[1]);
if (hp==0) error("Unknown host");
bcopy((char *)hp->h_addr,
(char *)&server.sin_addr,
hp->h_length);
server.sin_port = htons(atoi(argv[2]));
length=sizeof(struct sockaddr_in);
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n=sendto(sock,buffer,
strlen(buffer),0,(const struct sockaddr *)&server,length);
if (n < 0) error("Sendto");
n = recvfrom(sock,buffer,256,0,(struct sockaddr *)&from, &length);
if (n < 0) error("recvfrom");
write(1,"From server: ",13);
write(1,buffer,n);
close(sock);
return 0;
}
void error(const char *msg)
{
perror(msg);
exit(0);
}
I can't seem to even get the server to recognize a number even when I send a simple number, like 10. This part was working before but I must've changed something and I can't figure it out. I always get the "We can't compute!" response from the server.Code:while (1) {
n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
if (n < 0) error("recvfrom");
write(1,"Received a datagram: ",21);
write(1,buf,n);
for(int i = 0; i < strlen(buf); i++){
if(isdigit(buf[i])){
sum += buf[i] - '0';
printf("%d", sum);
}
else{
n = sendto(sock,"We can't compute!\n",19,0,(struct sockaddr *)&from,fromlen);
break;
}
}
//snprintf(buf, sizeof(buf), "%c", sum);
//n = sendto(sock,buf,128,0,(struct sockaddr *)&from,fromlen);
if (n < 0) error("sendto");
}
Also I am completely stumped on how to convert an integer to a char[]. I'm able to get the buffer from the client and convert it into an integer but I don't know how to convert it back to a char[] to send the sum back to the client. This is my attempt so far using a hard-coded buffer.
Any help would be appreciated.Code:int main(void) {
char buf[128] = "123456789";
int sum;
for(int i = 0; i < 128; i++){
if(isdigit(buf[i])){
sum += buf[i] - '0';
}
}
printf("%d\n", sum);
return 0;
}
