Merge pull request #49 from reedrosenbluth/docs/billboard

Fix billboard example contract

Author: lgalabru

examples/billboard/contracts/billboard.clar

@@ -1,10 +1,9 @@
-;; billboard v3
+;; billboard contract
 
 ;; error consts
-(define-constant ERR_INVALID_STRING u0)
-(define-constant ERR_STX_TRANSFER   u1)
+(define-constant ERR_STX_TRANSFER   u0)
 
-;; data maps/vars
+;; data vars
 (define-data-var billboard-message (string-utf8 500) u"Hello World!")
 (define-data-var price uint u100)
 
@@ -18,9 +17,19 @@
 )
 
 (define-public (set-message (message (string-utf8 500)))
-    (let ((cur-price (var-get price)))
+    (let ((cur-price (var-get price))
+          (new-price (+ u10 cur-price)))
+
+        ;; pay the contract
         (unwrap! (stx-transfer? cur-price tx-sender (as-contract tx-sender)) (err ERR_STX_TRANSFER))
-        (var-set price (+ cur-price u10))
-        (asserts! (var-set billboard-message message) (err ERR_INVALID_STRING))
+
+	;; update the billboard's message
+        (var-set billboard-message message)
+
+        ;; update the price of setting a message
+        (var-set price new-price)
+
+        ;; return the updated price
+	(ok new-price)
     )
 )