// 
// critical
//
#include <omp.h>
#include <stdio.h>
#include <math.h>

const int n=10000;
 
double f(double x)
{
	return 4/(x*x+1);
}

int main()
{
	double a=0.0, b=1.0;
	double h=(b-a)/n;
	double mysum, mypi=0.0;
	int i,tid;
	
	#pragma omp parallel num_threads(4) private(i,tid,mysum) shared(a,h,mypi)
	{
		tid = omp_get_thread_num(); 
		
		#pragma omp for
			for(i=1; i<n; i++)
			{
				mysum= mysum + f(a+i*h);
			}
		#pragma omp critical
			mypi = mypi + mysum;
	}
		
	mypi = mypi + (f(a) + f(b))/2;
	mypi = h*mypi;
	
	printf("mypi=%.10f, err=%.2e\n", mypi, fabs(mypi-4*atan(1)));

	return 0;
}