TCP

// SERVER SIDE :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

int main(){

  char *ip = "127.0.0.1";
  int port = 5566;

  int server_sock, client_sock;
  struct sockaddr_in server_addr, client_addr;
  socklen_t addr_size;
  char buffer[1024];
  int n;

  server_sock = socket(AF_INET, SOCK_STREAM, 0);
  if (server_sock < 0){
    perror("Socket error");
    exit(1);
  }
  printf("TCP server socket created.\n");

  memset(&server_addr, '\0', sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = port;
  server_addr.sin_addr.s_addr = inet_addr(ip);

  n = bind(server_sock, (struct sockaddr*)&server_addr, sizeof(server_addr));
  if (n < 0){
    perror("Bind error");
    exit(1);
  }
  printf("Bind to the port number: %d\n", port);

  listen(server_sock, 5);
  printf("Listening...\n");
  while(1){
    addr_size = sizeof(client_addr);
    client_sock = accept(server_sock, (struct sockaddr*)&client_addr, &addr_size);
    printf("Client connected.\n");

    bzero(buffer, 1024);
    recv(client_sock, buffer, sizeof(buffer), 0);
    printf("Client: %s\n", buffer);

    bzero(buffer, 1024);
    printf("Enter the Response.\n");
    gets(buffer);
    printf("Server: %s\n", buffer);
    send(client_sock, buffer, strlen(buffer), 0);

    close(client_sock);
    printf("Client disconnected.\n\n");
  }
  return 0;
}

// CLIENT SIDE:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

int main(){

  char *ip = "127.0.0.1";
  int port = 5566;

  int sock;
  struct sockaddr_in addr;
  socklen_t addr_size;
  char buffer[1024];
  int n;

  sock = socket(AF_INET, SOCK_STREAM, 0);
  if (sock < 0){
    perror("Socket error");
    exit(1);
  }
  printf("TCP server socket created.\n");

  memset(&addr, '\0', sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = port;
  addr.sin_addr.s_addr = inet_addr(ip);

  connect(sock, (struct sockaddr*)&addr, sizeof(addr));
  printf("Connected to the server.\n");
  printf("Enter the message to send.\n");
  bzero(buffer, 1024);
  gets(buffer);
  printf("Client: %s\n", buffer);
  send(sock, buffer, strlen(buffer), 0);

  bzero(buffer, 1024);
  recv(sock, buffer, sizeof(buffer), 0);
  printf("Server: %s\n", buffer);

  close(sock);
  printf("Disconnected from the server.\n");

  return 0;

}