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+# Chapter 11. Associative Containers
+
+## Exercise 11.1:
+>Describe the differences between a map and a vector.
+
+A `map` is a collection of key-value pairs. we can get a value **lookup by key** efficiently.
+
+A `vector` is a collection of objects, and every object has an **associated index**, which gives access to that object.
+
+## Exercise 11.2:
+>Give an example of when each of list, vector, deque, map, and set might be most useful.
+
+- list : a to-do list. always need insert or delete the elements anywhere.
+- vector : save some important associated data, always need query elements by index.
+- deque : message handle. FIFO.
+- map : dictionary.
+- set : bad_checks.
+
+## [Exercise 11.3 and 11.4](ex11_3_4.cpp)
+
+## Exercise 11.5:
+>Explain the difference between a map and a set. When might you use one or the other?
+
+- `set` : the element type is the **key type**.
+- `map` : we should use a key-value pair, such as `{key, value}` to indicate that the items together from one element in the map.
+
+I use `set` when i just need to store the `key`, In other hand, I　would like use `map` when i need to store a key-value pair.
+
+## Exercise 11.6:
+>Explain the difference between a set and a list. When might you use one or the other?
+
+`set` is unique and order, but `list` is neither. using which one depend on whether the elements are unique and order to store.
+
+## [Exercise 11.7](ex11_7.cpp)
+## [Exercise 11.8](ex11_8.cpp)