自己去改变x和n的值
// y=x-x^3/3!+x^5/5!-x^7/7!.... x=2.5,n=10,结果为:0.598472
#include <iostream>
using namespace std;
int main()
{
double x = 2.5;
int n = 10;
double sum = x;
double t = x;
for (double i = 2; i <= n; i++)
{
t *= (-1) * x * x / ((2 * i - 1) * (2 * i - 2));
sum += t;
}
cout << sum;
return 0;
}