Question on Maps in STL, Someone please explain, what exactly is happening here.! What is m[str[i]]..?

Question

#include <iostream>
#include<map>
using namespace std;
int main(){
string str = "hello";
map<int,int>m;
for(int i=0;i<str.length();i++){
m[str[i]]++;
if(m[str[i]]==2){
cout<<str[i]; }
}
}

Answer 1

It is iterating over string and finding frequency of characters in that string and as soon it get any any character freq = 2 it prints that character and keep on iterating over string.

In map<int, int> m, pair.first is of int type so probably ascii value of character is used and pair.second here is current frequency of that character.

Answer 2

m[str[i]]++; is increasing frequency of character str[i] by 1, it executes in every iteration. By default every key which is str[i] in this case is mapped with 0.
m[str[i]] == 2 is checking if current character is having frequency of 2 or not, if it has then print that character.

You can run below loop after previous loop to print frequency of h,e,l,o in string "hello" :
for(auto it:m){
cout<<it.first<<" "<<it.second<<endl;
}

map<char, int> would be better as you are only associating chatacter with their frequency and that map<int, int> is taking extra space.

Answer 3

Thanks man for helping. It's really nice this platform has someone who atleast responds.