求和问题

#include <stdio.h>
int main(void)
{
	int n;
	double sum=0.0000;
	printf("please input n:\n");
	scanf("%d",&n);
	printf("Output:\n");
	if(n<=0||n>=1000)
	{
		printf("Input error!\n");
	}else{
		printf("the ans is ");
		while(n>0){
			//printf("n=%d\n",n);
			if(n%2==1){
				sum+=(1.0000/n);
			//	printf("1234235\n");
			}else{
			//	printf("999999\n");
				sum-=(1.0000/n);
			}
		//	printf("sum=%lf\n",sum);
			--n;
		}
		printf("%.2lf\n",sum);
	}
	
	return 0;
}