note on prog lang prin

section 3

week 1

Recursive programming

Write a program to find sum of all elements in an array, without using loop (recursion only).  

You can use the size of the array as a parameter or the "last" element as 0 (sentinel).

pseudo code
   ax[n]
   i = 0
   s = 0
   while i < n
      s = s + ax[i]
      i++
   return s

recursive sum

invariant: s is the sum from 0 to i-1
this technique, s is called accumulating parameter

sum2(i, n, s)
  if i <= n return sum2( i+1, n, s + ax[i])
  else return s

sum(0, n)  ->  sum2(0, n, 0)

summary attendant 29,  good 25 (correct program), not-good 4
 
19 aug 2014