CODEWITHSUNDEEP
c++
SaladSnake
SaladSnake

Reputation: 167

C++ Find the most occurrence of a char using maps

I'm trying to find the most occurrence of char in a dat file. so if there are 24 e's in the file and 8 c's id like it to print out 'e'. I'm getting an error on the " * " of the int max var. The is the error:

Error 3 error C2440: 'initializing' : cannot convert from 'std::pair' to 'int' 

ifstream infile(filename);
    if (!infile.is_open()) return;    
    char x;
    map<char, int> count;
    while (infile >> x) count[x]++;
    for (auto it : count)    
        cout << it.first << " " << it.second << endl;
    int max = *max_element(count.begin(), count.end(), count.value_comp());
    cout << max << endl;
    return ' ';

as always any help is appreciated!

Upvotes: 1

Views: 486

Answers (3)

user2249683
user2249683

Reputation:

You have two issues

  • count.value_comp() compares the keys of map::value_type(s), which are pairs
  • max_element returns an iterator to a pair

You might change the code to:

#include <algorithm>
#include <iostream>
#include <fstream>
#include <map>

int main() {
    std::ifstream infile("filename");
    if (!infile.is_open())
        return 1;    // Check if file opened correctly
    char x;
    typedef std::map<char, int> map_type;
    map_type count;
    while (infile >> x) count[x]++;
    for (auto it : count)    // Pull this out of the while loop
        std::cout << it.first << " " << it.second << std::endl;
    auto less_count = [] (const map_type::value_type& a, const map_type::value_type& b) {
        return a.second < b.second;
    };
    auto max_pair = std::max_element(count.begin(), count.end(), less_count);
    int  max = max_pair->second;
    std::cout << max << std::endl;
}

Upvotes: 2

Slava
Slava

Reputation: 44258

When you dereference std::map::iterator you get std::pair and you try to assign it to int. Correct syntax would be:

int max = max_element(count.begin(), count.end(), count.value_comp())->second;

but you should check if there are elements in that map, otherwise you may dereference count.end() with UB. That would happen if file is empty for example.

Upvotes: 2

Abstraction
Abstraction

Reputation: 511

std::max_element will return ForwardIterator which in your case will be map<char,int>::iterator pointing to pair<char,int>. You have to change the last line to 

 int max = max_element(count.begin(), count.end(),count.value_comp())->second;

Upvotes: 2

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