Updated SC2039 (markdown)

SC2039.md

@@ -71,11 +71,13 @@ The POSIX standard does not allow for exponents.  However, you can replicate the
 
 ```sh
 pow () {
-    set $1 $2 1
-    while [ $2 -gt 0 ]; do
-      set $1 $(($2-1)) $(($1*$3))
+    set "$1" "$2" 1
+    while [ "$2" -gt 0 ]; do
+      set "$1" $(($2-1)) $(($1*$3))
     done
-    echo $3
+    # %d = signed decimal, %u = unsigned decimal
+    # Either should overflow to 0
+    printf "%d\n" "$3"
 }
 ```