示例代码 1：

/* 计算 1 - 1 / x + 1 / x * x - ... */

#include <stdio.h>
#include <sys/timeb.h>

int main(void)
{
	double x;
	int n;
	printf("Please input x and n: ");
	scanf_s("%lf%d", &x, &n);
	struct timeb t1;
	ftime(&t1);																/* 求得当前时间 */
	double totalSum = 1.0, subSum;
	for (int i = 1; i <= n; ++i) {
		subSum = 1.0;
		for (int j = 1; j <= i; ++j) {
			subSum = -subSum / x;
		}

		totalSum += subSum;
	}

	struct timeb t2;
	ftime(&t2);																/* 求得当前时间 */
	long t = (long)(t2.time - t1.time) * 1000 + (t2.millitm - t1.millitm);	/* 计算时间差 */
	printf("totalSum = %lf, 用时 %ld 毫秒\n", totalSum, t);

	return 0;
}

输出示例：

 

示例代码 2：

/* 计算 1 - 1 / x + 1 / x * x - ... */

#include <stdio.h>
#include <sys/timeb.h>

int main(void)
{
	double x;
	int n;
	printf("Please input x and n: ");
	scanf_s("%lf%d", &x, &n);
	struct timeb t1;
	ftime(&t1);																/* 求得当前时间 */
	double totalSum = 1.0, subSum = 1.0;
	for (int i = 1; i <= n; ++i) {
		subSum = -subSum / x;
		totalSum += subSum;
	}

	struct timeb t2;
	ftime(&t2);																/* 求得当前时间 */
	long t = (long)(t2.time - t1.time) * 1000 + (t2.millitm - t1.millitm);	/* 计算时间差 */
	printf("totalSum = %lf, 用时 %ld 毫秒\n", totalSum, t);

	return 0;
}

输出示例：