<code c hello.c> #include <stdio.h> #include <stdlib.h> #include <pthread.h>

This function will be executed by each thread void *print_hello_world(void *tid) { Print the thread's ID and a message

  printf("Hello World! Thread ID: %ld\n", (long)tid);
  pthread_exit(NULL);  // Exit the thread

}

int main(int argc, char *argv[]) {

  pthread_t threads[5]; // Array to store thread IDs
  int status;           // For storing return value of pthread_create
  long i;               // Loop variable

  // Create 5 threads
  for(i = 0; i < 5; i++) {
      printf("In main: creating thread %ld\n", i);
      // Create a new thread that will execute 'print_hello_world'
      status = pthread_create(&threads[i], NULL, print_hello_world, (void *)i);

      // Check for thread creation error
      if (status) {
          printf("Error in thread creation, return code: %d\n", status);
          exit(-1); // Exit if thread creation fails
      }
  }

  // Wait for all threads to complete
  for(i = 0; i < 5; i++) {
      pthread_join(threads[i], NULL);
  }

  printf("Program completed.\n");
  pthread_exit(NULL); // Exit the main thread

} </c>

This program creates 5 threads, each displaying a 'Hello World' message and its ID.
After the creation of all the threads, the main program (main) waits for each thread to finish before it concludes. It's important to note that error handling and thread synchronization are critical aspects when working with pthreads, in order to avoid race conditions and other concurrency issues.