> cat integral1.C

// file integral1.C, cs2223, D97/98 //
// random programming integration

// 14Apr98 NW, First version

// includes
#include "headers.h"

// definitions
#define NMAX 10000000

// prototype
float integrate (int, float, float, float, double (*) (double)); // random integration

// main()
int main ()
	{
	srand(time(NULL)); // seed the random number generator
	float pi = 4.0 * atan(1.0);
	float a = 0, b = pi/2, c = 1.0;
	for (int n = 1; n <= NMAX; n *= 10)
		{
		cout << "when n = " << n << " the integral = " << integrate(n,a,b,c,&sin) << endl;
		}
	return 0;
	} // end main()
	
float integrate(int n_points, float a, float b, float c, double (*fun) (double))
	{
	int counter = 0;
	float ratio = c * (b - a) / (float) n_points;
	while (n_points--)
		{
		float x = a + (b - a) * ((float) rand() / (float) RAND_MAX);
		float y = c * ((float) rand() / (float) RAND_MAX);
		if (y <= fun(x)) counter++;
		}
	return (float) counter * ratio; 
	} // end integrate()

// Copyright 1998 Norman Wittels

> g++ integral1.C

> a.out

when n = 1 the integral = 1.5708
when n = 10 the integral = 0.942478
when n = 100 the integral = 0.989602
when n = 1000 the integral = 1.00688
when n = 10000 the integral = 0.994942
when n = 100000 the integral = 0.995869
when n = 1000000 the integral = 1.00066
when n = 10000000 the integral = 0.999986