Update comments

c++.html.markdown

@@ -1027,7 +1027,6 @@ for (it = my_vector.begin(); it != my_vector.end(); ++it) {
 
 // Set
 // Sets are containers that store unique elements following a specific order.
-// For hash sets, use unordered_set. They are more effecient but do not preserve order.
 // Set is a very useful container to store unique values in sorted order
 // without any other functions or code.
 
@@ -1058,11 +1057,12 @@ cout << ST.size();  // will print the size of set ST
 // Output: 0
 
 // NOTE: for duplicate elements we can use multiset
+// NOTE: For hash sets, use unordered_set. They are more effecient but 
+// do not preserve order. unordered_set is available since C++11
 
 // Map
 // Maps store elements formed by a combination of a key value
 // and a mapped value, following a specific order.
-// For hash maps, use unordered_map. They are more effecient but do not preserve order.
 
 #include<map>
 map<char, int> mymap;  // Will initialize the map with key as char and value as int
@@ -1086,6 +1086,8 @@ cout << it->second;
 
 // Output: 26
 
+// NOTE: For hash maps, use unordered_map. They are more effecient but do 
+// not preserve order. unordered_map is available since C++11.
 
 ///////////////////////////////////
 // Logical and Bitwise operators