// Program to recursively compute the harmonic mean of an array of numbers.
// Program takes max 10 inputs,and stop reading the inputsas soon as a negative number is encounterd
// 
// Author:rahule@cse.iitk.ac.in

#include<stdio.h>
float harmonic_mean(int a[],int,int);	//function accpeting the array,lower bound,and total number of lements as arguement
main()
{
  int a[10],t,i=0,n;
  float hm;
  printf("\nEnter the numbers..\n");
  for(i=0;i<10;i++)	//scans every input till a negative input is encounterd
  {
    scanf("%d",&t);
    if(t<0)
      break;
    a[i]=t;
  }
  n=i;		//calculates total number of elements
  hm=harmonic_mean(a,0,n);	//initialy lower bound is set as 0
  printf("\nThe harmonic mean is %f\n ",hm);
}


float harmonic_mean(int a[],int i,int n)
 {
   if(i==n)		//base condition.i=n implies every elements has been processed
     return(0);
   if(i==0)
     return(n/((1/((float)a[i]))+harmonic_mean(a,i+1,n)));	//while returning to the "main",divide n by calculated sum  1/a[0] + 1/a[1] ...,and return
   else
   {
     return((1/((float)a[i]))+harmonic_mean(a,i+1,n));		//finds 1/a[1] + 1/a[2] + 1/a[3] ...
   }
 }