Recursion and Iteration

Question

What is the difference? Are these the same? If not, can someone please give me an example?

MW: Iteration - 1 : the action or a process of iterating or repeating: as

Answer 1

Here's a Lisp function for finding the length of a list. It is recursive:

(defun recursive-list-length (L)
  "A recursive implementation of list-length."
  (if (null L)
      0
    (1+ (recursive-list-length (rest L)))))

It reads "the length of a list is either 0 if that list is empty, or 1 plus the length of the sub-list starting with the second element).

And this is an implementation of strlen - the C function finding the length of a nul-terminated char* string. It is iterative:

size_t strlen(const char *s)
{
    size_t n;

    n = 0;
    while (*s++)
        n++;
    return(n);
}

You goal is to repeat some operation. Using iteration, you employ an explicit loop (like the while loop in the strlen code). Using recursion, your function calls itself with (usually) a smaller argument, and so on until a boundary condition (null L in the code above) is met. This also repeats the operation, but without an explicit loop.