/* 

   example4: Add all elements in an array in parallel. 


*/ 

#include <stdio.h> 


int main() {

  const int N=100; 
  int a[N]; 

  //initialize 
  for (int i=0; i<N; i++)
    a[i] = i; 


  //compute sum 
  int local_sum, sum; 
#pragma omp parallel private(local_sum) shared(sum) 
  { 
    local_sum =0; 
    
    //the array is distributde statically between threads
#pragma omp for schedule(static,1) 
    for (int i=0; i<N; i++) {
      local_sum += a[i]; 
    }

    //each thread calculated its local_sum. ALl threads have to add to
    //the global sum. It is critical that this operation is atomic.

#pragma omp critical 
    sum += local_sum;
  } 


  printf("sum=%d should be %d\n", sum, N*(N-1)/2);
}