formatting

lectures/15_maps_I/README.md

@@ -72,7 +72,7 @@ The mechanics of using std::pairs are relatively straightforward:
 - std::pairs are a templated struct with just two members, called first and second. Reminder: a struct
 is basically a wimpy class and in this course you aren’t allowed to create new structs. You should use classes
 instead.
-- To work with pairs, you must #include <utility>. Note that the header file for maps (#include <map>)
+- To work with pairs, you must #include &lt;utility&gt;. Note that the header file for maps (#include &lt;map&gt;)
 itself includes utility, so you don’t have to include utility explicitly when you use pairs with maps.
 - Here are simple examples of manipulating pairs:
 ```cpp
@@ -103,8 +103,12 @@ std::pair&lt;const key_type, value_type&gt;
 - We’ve used the [] operator on vectors, which is conceptually very simple because vectors are just resizable
 arrays. Arrays and vectors are efficient random access data structures.
 - But operator[] is actually a function call, so it can do things that aren’t so simple too, for example:
+
+```cpp
 ++counters[s];
- For maps, the [] operator searches the map for the pair containing the key (string) s.
+```
+
+- For maps, the [] operator searches the map for the pair containing the key (string) s.
   – If such a pair containing the key is not there, the operator:
     1. creates a pair containing the key and a default initialized value,
     2. inserts the pair into the map in the appropriate position, and