[C++] OpenMP težave

// OpenMP.cpp : Defines the entry point for the console application.
//

#include "stdlib.h"
#include "stdio.h"
#include "Windows.h"
#include "time.h"
#include "omp.h"
#define N 50000000
#define N_THREADS 2



int max_num(int a_size, int a[]){
	int i;
	int max = 0;

	for(i=0; i<a_size; i++){
		if(a[i] > max) max = a[i];
	}

	return max;
}

int max_num_p(int a_size, int a[]){
	int i, tn, max[N_THREADS];
	//omp_set_num_threads(N_THREADS);

	#pragma omp parallel for shared(a,max) private(tn)
	for(i=0; i<a_size; i++){
		//if(i==1)printf("Num: %d\n", omp_get_num_threads());
		tn = omp_get_thread_num();
		//printf("Thread %d - i=%d\n", tn, i);
		if(max[tn]<a[i]){
			max[tn]=a[i];
		}
	}

	/*for(i=0; i<N_THREADS; i++){
		printf("%d\n", max[i]);
	}*/
	return max_num(N_THREADS, max);
}

void fill_random(int a_size, int a[]){
	int i;
	srand( time(NULL) );
	for(i=0; i<a_size; i++){
		a[i]=rand();
	}
}

int main(int argc, char * argv[])
{
	int start,stop, time;
	
	int * a;
	a = (int *)malloc(N * sizeof(int));
	int max;

	fill_random(N, a);
	printf("Start:\n");
	start = clock();
		max = max_num(N, a);
	stop = clock();
	time = stop-start;

	printf("%d t:%d\n", max, time);

	start = clock();
		max = max_num_p(N, a);
	stop = clock();
	time = stop-start;

	printf("%d t:%d\n", max, time);
	
	free(a);
	system("pause");
	return 0;
}

int max_num_p(int a_size, int a[]){
	int i, tn, max[N_THREADS];
	omp_set_num_threads(N_THREADS);

	#pragma omp parallel private(tn)
	{
		tn = omp_get_thread_num();
		#pragma omp for
		for(i=0; i<a_size; i++){
			if(max[tn]<a[i]) max[tn]=a[i];
		}
	}

	return max_num(N_THREADS, max);
}