Update examples

Some examples had syntax errors; those have been fixed. Additionally,
I added a simple example with a while loop. It does not contain a proper
post-condition either, which might be interesting as well (as the
program might be able to handle those properly too).

examples/abs

 abs ( x : int | y : int ) {
     assume x > 0;
-    if x[ 0 ] < 0 then y := 0 else skip ;
+    if x < 0 then { y := 0 } else { skip; skip; skip; skip } ;
     assert y > 0
 }
 

examples/memberOf

@@ -5,9 +5,9 @@ memberOf ( x : int , a :[] int | found : bool ) {
         k := 0 ;
         found := false ;
         while k <# a do {
-            if a [ k ]= x then found := true else skip ;
+            if a [ k ]= x then { found := true } else { skip } ;
             k := k +1
         }
     };
     assert found
-}
\ No newline at end of file
+}

examples/sumArray

+sumArray(arr: []int, first: int, last: int | sum: int) {
+    assume (first >= 0 && last < #arr && first < last);
+    sum := 0;
+    current := first;
+
+    while (current <= last) do {
+        sum := sum + arr[current];
+        current := current + 1
+    }
+
+}
+