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

main()
{
  int pid, status, i;
  char *newargv[4];
  newargv[0] = "cal";
  newargv[1] = "9";
  newargv[2] = "2020";
  newargv[3] = NULL;

  pid = fork();

  if (pid == 0)
  {
    /*
    for (i = 0; i < 1000000000; ++i)
      ;

    printf ("I'm in the child.  My process number is %d.\n", getpid());
    printf ("%d\n", *((int *) 0));
    */
    status = execv("/usr/bin/cal", newargv);
    //status = execv("aaaa", newargv);
    printf("execv returned %d\n", status);
  }
  else
  {
    wait(& status);
    printf ("I'm in the parent.  My process number is %d.\n", getpid());

    // Look at section 2 man page for wait for details:  man -s 2 wait
    if (WIFEXITED(status))
      printf("Child terminated normally.\n");
    else if(WIFSIGNALED(status))
      printf("Child was terminated by a signal.\n");
  }
}