方法1.pow函数型

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
	int i = 0;
	double sum = 0;
	for (i = 1; i <= 100; i++)
	{
		sum += (pow(-1, i+1) * 1 / i); // pow（x,y）,计算x的y次方，x、y及函数值均为double型
	}
	printf("sum=%lf\n", sum); //打印浮点型
	system("pause");
	return 0;
}

方法2.数学型

#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i = 0;
	double sum= 0.0;
	for (i = 1; i <= 100; i++)
	{
		if (i % 2 != 0)
		{
			sum += (1.0 / i); //左右两边类型应该保持一致
		}
	    if (i % 2 == 0)
		{
			sum -= (1.0 / i);
		}		
	}
	printf("sum=%lf\n", sum);
	system("pause");
	return 0;
}

方法3.1.for循环

#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i = 1;
	float sign = 1.0; sum = 0.0;
	for (i = 1; i <= 100; i++)
	{
		sum += sign / i;
		sign = -sign;
	}
	printf("sum=%f\n", sum);
	system("pause");
	return 0;
}

方法3.2.while循环

#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i = 1;
	float  sum = 0.0, sign = -1;
	while (i <= 100)
	{
		sign = -sign;
		sum += sign/i;
		i++;
	}
	printf("sum=%lf\n", sum);
	system("pause");
	return 0;
}

方法3.3.do...while循环

#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i = 1;
	float  sum = 0.0, sign = -1;
	do
	{
		sign = -sign;
		sum += sign / i;
		i++;
	} 
        while (i <= 100);
	printf("sum=%lf\n", sum);
	system("pause");
	return 0;
}