// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT 8008
#define RECIEVE_BUFFER_SIZE 1024
const char* responseMessage = "Hello from server";

// Driver code
int main() {

        //Create a UDP socket
        //int socket(int domain, int type, int protocol);
        //Domain is the place where the data goes. AF_BLUETOOTH, AF_INET6, AF_UNIX is local communication between different programs
        //Type is the type of connection, so connection based (TCP), connectionless (UDP) or somewhere in between or beyond
        //Protocol is an enum or flags that give some more options specific to that type. For SOCK_STREAM, you can force it to use SCTP instead of TCP. For SOCK_RAW, it can give you control over the ip frame, and even the ethernet frame.
        //So this function makes a file descriptor to an IPV4 UDP 'connection' with no options.
        int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
        // Creating socket file descriptor
        if ( sockfd < 0) {
                perror("socket creation failed");
                exit(EXIT_FAILURE);
        }


        struct sockaddr_in serverAddress;
        memset(&serverAddress, 0, sizeof(serverAddress));

        // Filling server information
        serverAddress.sin_family = AF_INET; // IPv4
        serverAddress.sin_addr.s_addr = INADDR_ANY;
        serverAddress.sin_port = htons(PORT);

        // Bind the socket with the server address
        if(bind(sockfd, (const struct sockaddr*)&serverAddress, sizeof(serverAddress))){        //Bind returns 0 if succeeded, or -1 if failed. -1 is still true.
                perror("bind failed");
                exit(EXIT_FAILURE);
        }

        struct sockaddr_in clientAddress; unsigned int clientAddressSize = sizeof(clientAddress);
        memset(&clientAddress, 0, clientAddressSize);

        char buffer[RECIEVE_BUFFER_SIZE];
        int bytesRecieved = recvfrom(sockfd, (char*)buffer, RECIEVE_BUFFER_SIZE, MSG_WAITALL, (struct sockaddr*) &clientAddress, &clientAddressSize); //sets clientAddress to the client's address and the new size
        buffer[bytesRecieved] = '\0';
        printf("Client : %s\n", buffer);

        sendto(sockfd, (const char*)responseMessage, strlen(responseMessage), MSG_CONFIRM, (const struct sockaddr*) &clientAddress, clientAddressSize);
        printf("Hello message sent.\n");

        return 0;
}

#include <stdio.h>
#include <stdlib.h>
int main(){

  int * int_ptr;
  int_ptr = (int *)malloc(2*sizeof(int));
  
  if(!int_ptr) {
    printf("Something went wrong while allocating memory. Exiting...");
    exit(1);
  }
  
  printf("Enter first integer: ");
  scanf("%i", &int_ptr[0]);
  
  printf("Enter second integer: ");
  scanf("%i", &int_ptr[1]);
  
  printf("Original values: 1st = %i 2nd = %i\n",int_ptr[0], int_ptr[1]);
  
  int_ptr[0] = int_ptr[0] ^ int_ptr[1];
  //printf("%i\n", int_ptr[0]);
  int_ptr[1] = int_ptr[0] ^ int_ptr[1];
  //printf("%i\n", int_ptr[1]);
  int_ptr[0] = int_ptr[0] ^ int_ptr[1];
  //printf("%i\n", int_ptr[0]);
  
  printf("Swapped values: 1st = %i 2nd = %i\n", int_ptr[0], int_ptr[1]);

  free(int_ptr);
  exit(0);
}

#include <stdio.h>
#include <unistd.h>

int main() {
  char * cmd[] = {
    "who",
    "ls",
    "date"
  };
  int i;
  printf("0=who 1=ls 2=date : ");
  scanf("%d", & i);
  execlp(cmd[i], cmd[i], (char * ) 0);
  printf("execlp failed\n");
  return 0;
}

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
  pid_t pid; /* could be int */
  int i;
  pid = fork();
  printf("PID=%d\n", pid);
  if (pid > 0) {
    /* parent */
    for (i = 0; i < 10; i++)
      printf("\t\t\tPARENT %d\n", i);
  } else {
    /* child */
    for (i = 0; i < 10; i++)
      printf("CHILD %d\n", i);
  }
  return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int main() {
  char * cmd[] = {
    "who",
    "ls",
    "date"
  };
  int i;
  while (1) {
    printf("0=who 1=ls 2=date : ");
    scanf("%d", & i);
    if (fork() == 0) {
      /* child */
      execlp(cmd[i], cmd[i], (char * ) 0);
      printf("execlp failed\n");
      exit(1);
    } else {
      /* parent */
      wait((int * ) 0);
      printf("child finished\n");
    }
  } /* while */
} /* main */

#include <stdio.h>
#include <stdlib.h>

calculate(a, b)
int a;
int b;
{
        printf("%d", a+b);
}

main(argc, argv)
int argc;
char** argv;
{
        if(argc < 3){
                return 0;
        }
        calculate(atoi(argv[1]), atoi(argv[2]));
}