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;}