Solution C

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
int main()
{
   // freopen("in","r",stdin);
   // freopen("out","w",stdout);



	int  n=1;
	//while(scanf("%d",&n )!=EOF){

 	   double term = 1.0, sign = 1,sum = 0;

	   while (fabs(term) >= 1e-4)
	   {
		term = sign / n;
		sum = sum + term;
		sign = -sign;
		n++;
	   }
	    printf("%lf\n", sum);
	//}
  return 0;
}

Solution C++

#include<stdio.h>
#include<math.h>
int main()
{
	double sum = 0.0 ,i;
	for(i = 1.0;fabs(1/i) > 1e-4;i++)
	{
		sum = sum + 1/(i*pow(-1,i + 1));
	}
	printf("%0.6lf\n",sum);
	return 0;
}