// SumOfOdds.C
// Mon Feb 10 13:20:22 EST 1997
// Burt Rosenberg

// This program demonstrates recursion.

#include<iostream.h>

int sumOfOdds(int largestOdd)
{
   //ASSERT: largestOdd should be a positive odd number
  
   if (largestOdd<=1) 
   {
      return 1 ; // base case of recursion
   }
   else
   {
      // else apply formulat S_i = S_{i-1} + o_i
      // where o_i is the i-th odd number, and S_j is
      // the sum of the first j odd numbers.

      return ( sumOfOdds( largestOdd-2 ) + largestOdd ) ;
   }
}  // end of function sumOfOdds

void main()
{
   int numberOfOdds ;

   // the polite part: prompt for input, set up
   // for output.
   cout << "Enter the number of odds to add: " ;
   cin >> numberOfOdds ;
   cout << "The sum of the first " << numberOfOdds <<
      " odd numbers is: " ;

   if ( numberOfOdds <=0 ) 
   {
       cout << 0 ;
   }
   else
   {
       // the formula for o_i, the i-th odd, is
       //    o_i = 2*i-1

       cout << sumOfOdds( 2*numberOfOdds - 1 ) ;
   }

   // add a newline to the output.
   cout << endl ;

}