SERVER

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

int main(int argc, char* argvs[]){

    if(argc != 2){
    printf("Este necesar portul!\n" );
        return 1;
  }

    int s,c,l;
    int i = 0;
    char sir[50]="", fin[]="SUCCES",finm[]="succes",car;
    int p[2]; pipe(p);
    struct sockaddr_in server, client;
    int port = atoi(argvs[1]);

    //VERIFICARE---------
    if(port<1024 || port>65535){
        printf("Portul nu convine!\n");
        return 1;
    }
    //VERIFICARE---------

    s = socket(AF_INET, SOCK_STREAM, 0);
    if(s<0){
        printf("Eroare socket server!\n");
        return 1;
    }

    memset(&server, 0, sizeof(server));
    server.sin_port = htons(port);
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;

    if(bind(s,(struct sockaddr *) &server ,sizeof(server))<0){
        printf("Eroare la bind!\n");
        return 1;
    }

    listen(s,5);

    l = sizeof(client);
    memset(&client,0,sizeof(client));
    while(1){
        c=accept(s,(struct sockaddr *) &client, &l);
        printf("S-a conectat un client\n");
        if(fork()==0){
            //char car;
            recv(c,&car,sizeof(car),MSG_WAITALL);
            write(p[1],&car,sizeof(char));
            close(p[0]);close(p[1]);
            close(c);
            return 0;
        }
        read(p[0],&car,sizeof(char));
        sir[strlen(sir)] = car;
        printf("%s\n",sir);
        if(strcmp(sir,fin)==0 || strcmp(sir,finm)==0){
            close(p[0]);close(p[1]);
            break;
        }
    }
    return 0;
}


CLIENT ----------------------------------------------------------

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

int main(int argc, char* argvs[]){
  if(argc != 3){
    printf("Este necesar ip-ul si portul!\n" );
    return 0;
  }

  int c;
  struct sockaddr_in server;
  char ip[20];
  strcpy(ip,argvs[1]);
  int port = atoi(argvs[2]);


  //VERIFICARI-------------------

  if(port<1024 || port>65535){
    printf("Portul nu convine!\n");
    return 1;
  }
  char verif[]="0123456789.";
  int i=0;
  for(i=0;i<strlen(ip);i++){
    if(strchr(verif,ip[i])==0){
      printf("Ip-ul nu convine!\n");
      return 1; //eroare
    }
  }
  //VERIFICARI------------------

  c = socket(AF_INET, SOCK_STREAM, 0);
  if(c<0){
    printf("Eroare socket client!\n");
    return 1;
  }

  memset(&server, 0 ,sizeof(server));
  server.sin_port = htons(port);
  server.sin_family = AF_INET;
  server.sin_addr.s_addr = inet_addr(ip);

  if (connect(c, (struct sockaddr *) &server, sizeof(server)) < 0) {
    printf("Eroare conectarea la server!\n");
    return 1;
  }
  char car;
  printf("Introduceti caracterul: " );
  scanf("%c",&car);

  if(car<65){
    printf("Nu e litera!\n");
    return 0;
  }
  else{
    if(car>90){
      if(car<97 || car>122){
        printf("Nu e litera!\n");
        return 0;
      }
    }
  }
  send(c,&car,sizeof(car),0);
  close(c);
}