thread shit

#include <iostream>
#include <pthread.h>
#include <time.h>


#define MAX 20
#define THREAD_MAX 4

using namespace std;
int a[MAX];
int part = 0;
void merge(int start, int mid, int end){
	int* left = new int[mid - start + 1];
	int* right = new int[end - mid];
	int n1 = mid - start + 1, n2 = end - mid, i, j;
	for (i = 0; i < n1; i++)
		left[i] = a[i + start];

	for (i = 0; i < n2; i++)
		right[i] = a[i + mid + 1];

	int k = start;
	i = j = 0;

	while (i < n1 && j < n2) {
		if (left[i] <= right[j])
			a[k++] = left[i++];
		else
			a[k++] = right[j++];
	}
	while (i < n1) {
		a[k++] = left[i++];
	}
	while (j < n2) {
		a[k++] = right[j++];
	}
}


void merge_sort(int start, int end){
	int mid = start + (end - start) / 2;
	if (start < end) {
		merge_sort(start, mid);
		merge_sort(mid + 1, end);
		merge(start, mid, end);
	}
}


void* merge_sort(void* arg){
	int thread_part = part++;
	int start = thread_part * (MAX / 4);
	int end = (thread_part + 1) * (MAX / 4) - 1;
	int mid = start + (end - start) / 2;
	if (start < end) {
		merge_sort(start, mid);
		merge_sort(mid + 1, end);
		merge(start, mid, end);
	}
	return 0;
}


int main()
{
	
	for (int i = 0; i < MAX; i++)
		a[i] = rand() % 100;
		
	pthread_t threads[THREAD_MAX];
	for (int i = 0; i < THREAD_MAX; i++)
		pthread_create(&threads[i], NULL, merge_sort,(void*)NULL);
		
	for (int i = 0; i < 4; i++)
		pthread_join(threads[i], NULL);

// 	for(int i = 0; i < MAX; i++){
// 	    cout<< a[i] << " ";
// 	}
	    
	merge(0, (MAX / 2 - 1) / 2, MAX / 2 - 1);
	merge(MAX / 2, MAX/2 + (MAX-1-MAX/2)/2, MAX - 1);
	merge(0, (MAX - 1)/2, MAX - 1);
	cout << "\nSorted array: ";
	for (int i = 0; i < MAX; i++)
		cout << a[i] << " ";
		
	return 0;
}