Use case for std::map: counting instances of something

map_counting.cc

#include <iostream>
#include <string>
#include <map>
#include <vector>

int main()
{
    // a map is a really good way to keep track of information.
    // if the key doesn't exist, it will be created.
    // if the key does exist, it will just reassign the value
    // or add one to the value.
    std::map<std::string, int> myMap;
    myMap["hello"] = 1;
    myMap["hello"]++;
    myMap["world"]++;
    for (auto i=myMap.begin(); i!=myMap.end(); i++ ){
        std::cout << i->first << ", " << i->second << std::endl;
    }
    // output:
    // hello, 2
    // world, 1
    
    myMap.clear();
    
    // example: word counter
    std::vector<std::string> words = {"foo", "bar", "foo", "hello", "world", "foo", "bar", "world", "foo"};
    for (const auto& word : words) {
        myMap[word]++;
    }
    for (auto i=myMap.begin(); i!=myMap.end(); i++ ){
        std::cout << i->first << ", " << i->second << std::endl;
    }
    // output:
    // bar, 2
    // foo, 4
    // hello, 1
    // world, 2
}