17.求圆周率PI: PI/4 = 1- 1/3 + 1/5 -1/7 +.....

#include<iostream>
using namespace std;
int YuanZhou(int);
 
int main()
{
    int n;
    double temp,sum=0;
    cout<<"please input an number: "<<endl;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        if(i%2==0)
        {
            temp=(-1.0/YuanZhou(i));//两个int型相除得到的结果会自动变成int型
        }else
        {
            temp=(1.0/YuanZhou(i));//隐式类型转换
        }
        sum+=temp;
    }
    cout<<4*sum<<endl;
    return 0;
}
 
int YuanZhou(int index)
{
    if(index<0)
    {
        return -1;
    }else
    {
        return (2*index-1);
    }
}

#include<iostream>
#include<iomanip>
#include<cmath>
 
using namespace std;
int main()
{
double item=1, sum=0;
for(int n=1;fabs(item)>1e-6;n++)
{
      sum+=item;
  item*=(-1.0)*(2*n-1)/(2*n+1);
}
 
cout<<"Pi= "<<setiosflags(ios::fixed)<<setprecision(6)<<sum*4<<endl;
 
}