C/Visual C - Algoritmo que calcule la sumatoria

#include <math.h>

  //3/2 - 5/4 + 7/8 -9/16 + 11/32 -13/64+..................

  double dSum = 0.;

  int n, d;

  n = 3;

  d = 2;

  dSum = (double)3/(double)2;

  for(int i=1; i<30; i++){

      n = abs(n) + 2;

      d *= 2;

      if(fmod((double)i, 2.) != 0.)

         n *= -1;

      dSum += (double)n/(double)d;

     }