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

/*
 * A simple demo of using fork, exec, and waitpid.
 */
int main() {
  printf("program started\n");

  pid_t pid = fork(); // make a child process

  if (pid < 0) {
    printf("fork failed\n");
  } else if (pid == 0) {
    // child process
    
    printf("this is the child process\n");

    // run some other program
    if (execlp("/bin/pwd", "/bin/pwd", NULL) < 0) {
      printf("exec failed\n");
    }

    // will never reach here

  } else {
    // parent process

    printf("this is the parent process (child pid is %d)\n", pid);

    int child_status;
    if (waitpid(pid, &child_status, 0) < 0) {
      printf("waitpid failed\n");
      exit(1);
    }

    printf("child process is reaped\n");

  }

  printf("program ending\n");

  return 0;
}