1/3-3/5+5/7-7/9…+19/21）的和

#include<iostream>
using namespace std;
int main()
{
double i,j,n;
double sum,k;
i=1;
j=3;
n=1;
sum=0,k=0;
while(i<=19)
{
k=(i/j)*n;
sum=sum+k;
n=-n;
i=i+2;
j=j+2;
}

cout<<sum<<endl;

return 0;
}