Find number of occurrences in a map C++ - c++

Question

I am trying to create a map in C++ and I will use it to compare wheater a vector of string match another one. The condition is that only one word can be taken into consideration. For example, given:
{"two", "times", "three", "is", "not", "four"}
{"two", "times", "two", "is", "four"}
In this case they shouldn't match because there is only one "two" in the first vector.
My code is as follows:
#include <iostream>
#include <vector>
#include <map>
using namespace std;
void checkMagazine(vector<string> magazineWords, vector<string> noteWords)
{
map<string, int> magazine;
map<string, int>::iterator it = magazine.begin();
//populating the map
for (string magazineWordString : magazineWords)
{
it = magazine.find(magazineWordString);
if (it != magazine.end())
{
int numberOfOccurences = it->second;
magazine.insert(pair<string, int>(magazineWordString, numberOfOccurences + 1));
}
else
{
magazine.insert(pair<string, int>(magazineWordString, 1));
}
}
//checking for correspondences
for (string noteWordString : noteWords)
{
it = magazine.find(noteWordString);
if (it != magazine.end())
{
int numOfOccurences = it->second;
magazine.insert(pair<string, int>(noteWordString, numOfOccurences - 1));
}
else
{
cout << "There is no match." << endl;
return;
}
}
cout << "There is a match!" << endl;
}

Answer 1

There's a far easier way! The subscript operator on a map will try to find the key in the map. If it is successful, it returns a reference to its value. Otherwise, it creates a new key/value pair for you on the spot and gives you a reference to its value.
So since the default value of an int will be 0 (that is, when we create a new key/value pair, the value will be 0), all your work can actually just be:
bool checkMagazine(vector<string> magazineWords, vector<string> noteWords)
{
map<string, int> bank;
//populating the map
for (string magazineWord : magazineWords) {
++bank[magazineWord];
}
//checking for correspondences
for (string noteWord : noteWords) {
if(--bank[noteWord] < 0) { return false; }
}
return true;
}
Watch it run here: https://ideone.com/MzLAJM