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);
    }
}