第5章例5-3

#include<stdio.h>
#include<math.h>
int main(void)
{
	double e,pi;
	double funpi(double e);

	printf("Enter e:");
	scanf("%lf",&e);
	pi = funpi(e);
	printf("pi=%f\n",pi);

	return 0;
}

double funpi(double e)
{
	int denominator,flag;
	double item,sum;

	flag = 1;
	denominator = 1;
	item = 1.0;
	sum = 0;

	while(fabs(item)>=e){
		item = flag*1.0/denominator;
		sum = sum + item;
		flag = -flag;
		denominator = denominator + 2;
	}

	return sum*4;
}