c++ how to make map code example

Example 1: map vs unordered_map in C++

| map             | unordered_map
---------------------------------------------------------
Ordering        | increasing  order   | no ordering
                | (by default)        |

Implementation  | Self balancing BST  | Hash Table
                | like Red-Black Tree |  

search time     | log(n)              | O(1) -> Average 
                |                     | O(n) -> Worst Case

Insertion time  | log(n) + Rebalance  | Same as search
                      
Deletion time   | log(n) + Rebalance  | Same as search


::-> Use std::map when
1. You need ordered data.
2. You would have to print/access the data (in sorted order).
3. You need predecessor/successor of elements.
  
::-> Use std::unordered_map when
1. You need to keep count of some data (Example – strings) and no ordering is required.
2. You need single element access i.e. no traversal.

Example 2: map declaration c++

//assuming your variables are called : variables_
#include <map>
#include <string>

std::map<int, std::string> map_;
map_[1] = "mercury";
map_[2] = "mars";
map_.insert(std::make_pair(3, "earth"));
//either synthax works to declare a new entry

return map_[2]; //here, map_[2] will return "mars"