1-1/2+1/3-1/4+1/5-1/6...+1/99-1/100

#include<stdio.h>

int main()

{

	int i = 0;

	double sum1 = 0.0;

	double sum2 = 0.0;

	double sum3 = 0.0;

	double sum4 = 0.0;

	double sum5 = 0.0;

	for (i = 1; i <= 100; i++)

	{

  sum1 = 1.0 / i;

  sum2 = sum2 + sum1;

	}

	for (i = 2; i <= 100; i += 2)

	{

  sum3 = 1.0 / i;

  sum4 = sum3 + sum4;

	}

	sum5 = sum2 - sum4*2;

	printf("%lf",sum5);

	return 0;

}

代码还可以优化：

#include<stdio.h>

int main()

{

	int i = 0;

	double sum1 = 0.0;

	int fu = 1;

	for (i = 1; i <= 100; i++)

	{

  sum1 += fu*1.0 / i;

  fu = -fu;

	}

	printf("%lf",sum1);
return 0;
}