求助！C语言编程题 6

#include "stdafx.h"

int _tmain(int argc, _TCHAR* argv[])
{
int i; double sum=0;
scanf("%d",&i);
for(int k=1;k<=i;k++)
{
if(i<1)
{
printf("请输入正整数！");
}

if(k%2==1)
{
double d=k;
sum+=1/d;
}
else
{
double c=k;
sum=sum-1/c;
}

}
printf("%f",sum);
}