Define variable local to function

I am working (joyfully) through the Introduction to Emacs Lisp Programming and have solved the first 8.7 Searching Exercise. It states,

Write an interactive function that searches for a string. If the search finds the string, leave point after it and display a message that says “Found!”.

My solution is

(defun test-search (string)
  "Searches for STRING in document.
Displays message 'Found!' or 'Not found...'"
  (interactive "sEnter search word: ")
  (save-excursion
    (beginning-of-buffer)
    (setq found (search-forward string nil t nil))) 
  (if found
      (progn
        (goto-char found)
        (message "Found!"))
    (message "Not found...")))

How do I make found be local to the function? I know that a let statement defines a local variable. However, I only want to move point if the string is found. It's not clear to me how to define found locally, yet not have the point be set to the beginning-of-buffer if the string isn't found. Is let the proper command for this situation?

Solution

As stated in some comments, let is what you want to use here, although it will not define a variable local to the function, but a scope of its own.

Your code becomes:

(defun test-search (string)
   "Searches for STRING in document.
Displays message 'Found!' or 'Not found...'"
   (interactive "sEnter search word: ")
   (let ((found (save-excursion
                  (goto-char (point-min))
                  (search-forward string nil t nil))))
     (if found
       (progn
         (goto-char found)
         (message "Found!"))
       (message "Not found..."))))

Edit: code modified thanks to phils'comment.