一个简单的C++求pi值得问题

Question

//为什么输出的结果不对？

#include
using namespace std;
int main()
{
double pi=0;
int i;
for(i=0;1.0/(2*i+1)>=0.0001;++i)
{
if(i%2==0)
pi=pi+4.0/(2*i+1);
else
pi=pi-4.0*(1.0/(2*i+1));
}
cout<<"pi = "<<pi<<endl;
cout<<"count = "<<i<<endl;
return 0;
}

Answer 1

#include <iostream>
using namespace std;
int main()
{
    double pi=0;
    int i;
    for(i=0;1.0/(2*i+1)>=0.0001;++i)
    {
        if(i%2==0)
            pi=pi+4.0/(double)(2*i+1); //改
        else
            pi=pi-4.0*(1.0/(double)(2*i+1)); //改
    }
    cout<<"pi = "<<pi<<endl;
    cout<<"count = "<<i<<endl;
    return 0;
} 

pi = 3.14139
count = 5000