Fix Objective-C implementation, it has different result comparing to others.

Division operator and modulo operator have the same priority. So the result of "i % sizeof(key)/sizeof(unichar)" is the same as "(i % sizeof(key)) / sizeof(unichar)". But expected result should be "i % (sizeof(key)/sizeof(unichar))".

Objective-C/main.m

@@ -19,7 +19,7 @@
     
     for(int i = 0; i < input.length; i++) {
         unichar c = [input characterAtIndex:i];
-        c ^= key[i % sizeof(key)/sizeof(unichar)];
+        c ^= key[i % (sizeof(key)/sizeof(unichar))];
         [output appendString:[NSString stringWithFormat:@"%C", c]];
     }