#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 <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 <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 <assert.h>
#include <signal.h>

void myHandler(int iSig) {
  printf("In myHandler with argument %d\n", iSig);
}
int main() {
  void( * pfRet)(int) = signal(SIGINT, myHandler);
  assert(pfRet != SIG_ERR);
  printf("Entering an infinite loop\n");
  while (1) {
    printf(".");
  }
  return 0; // use CTRL+\ to exit
}

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

int glbvar = 6;
int main() {
  int locvar = 88;
  pid_t pid;
  printf("Before fork()\n");
  if ((pid = fork()) == 0) {
    /* child */
    glbvar++;
    locvar++;
  } else if (pid > 0) {
    /* parent */
    sleep(2);
  } else
    perror("fork error");
  printf("pid=%d, glbvar=%d, locvar=%d\n", getpid(), glbvar, locvar);
  return 0;
} /* end 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]));
}