text:   
  //compilation instruction:
  //gcc -g omp_hello.c -fopenmp 
  //./a.out
  /******************************************************************************
  
  
  #include <omp.h>
  #include <stdio.h>
  #include <stdlib.h>
  
  int main (int argc, char *argv[])
  {
  int nthreads, tid;
  
  /* Fork a team of threads giving them their own copies of variables */
  #pragma omp parallel private(nthreads, tid)
    {
  
    /* Obtain thread number */
    tid = omp_get_thread_num();
    printf("Hello World from thread = %d\n", tid);
  
    /* Only master thread does this */
    if (tid == 0)
      {
      nthreads = omp_get_num_threads();
      printf("Number of threads = %d\n", nthreads);
      }
  
    }  /* All threads join master thread and disband */