/* Program to check whether a sum converges well */

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

double sumfunc(int N1, int N2, int increment,double (*function)(double))
{
  int i;
  double tally,current_val;
  tally=0.0;
  for (i=N1;i!=(N2+increment);i=i+increment) 
/*This condition allows us to go forward or backwards.  
We stop when we get to the point where we have gone past 
the target value*/
    {
      current_val=i*1.0;
      tally=tally+(*function)(current_val);
/*The *function expression here allows us to change the program easily
to consider other functions.*/
    }
  return(tally);
}

double one_over_x(double x)
{
  double value;
  value=1.0/x;
}


main()
{
  int imin,imax;
  double x,sum1,sum2;
  printf("What is the minimum value for the variable?\n");
  scanf("%i",&imin);
  printf("What is the maximum value for the variable?\n");
  scanf("%i",&imax);
  sum1=sumfunc(imin,imax,+1,&one_over_x);
  printf("Going forward the sum is %lf \n", sum1);
  sum2=sumfunc(imax,imin,-1,&one_over_x);
  printf("Going backward the sum is\n %lf \n", sum2);
  printf("The difference is %lf\n",fabs(sum1-sum2));
  printf("The difference times N is %lf\n",(imax-imin+1)*fabs(sum1-sum2));

}