第二题

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

	scanf("%lf",&n);
	
	if((n<3)&&(n>8))
		printf("Error!");
	else if(n==0)
		return 0;
	else if((n>=3)&&(n<=8))
		pi=funpi(n);
	scanf("%lf",&pi);

	return 0;
}
double funpi(double n)
{
	int denominator,flag;
	double item,sum;

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

	while(fabs(item)>=pow(10,-n)){
		item=flag*1.0/denominator;
		sum=sum+item;
		flag=-flag;
		denominator=denominator+2;
	}
	return sum*4;
}