C++ Maps

What is a Map?

A map stores key-value pairs where each key is unique and automatically sorted. Include <map>.

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main() {
    map<string, int> wordCount;

    wordCount["hello"]  = 3;
    wordCount["world"]  = 2;
    wordCount["cpp"]    = 5;
    wordCount["hello"]++;   // increment existing

    for (const auto& [word, count] : wordCount) {
        cout << word << ": " << count << endl;
    }
    cout << "Contains 'cpp': " << wordCount.count("cpp") << endl;
    return 0;
}

Output (sorted by key):

cpp: 5
hello: 4
world: 2
Contains 'cpp': 1

Map Operations

map<string, string> capitals;
capitals["Cambodia"] = "Phnom Penh";
capitals["France"]   = "Paris";
capitals["Japan"]    = "Tokyo";

if (capitals.find("Japan") != capitals.end())
    cout << "Japan capital: " << capitals["Japan"] << endl;

capitals.erase("France");
cout << "Size: " << capitals.size() << endl;   // 2

#include <iostream>
#include <map>
#include <sstream>
using namespace std;

int main() {
    string line, word;
    cout << "Enter text: ";
    getline(cin, line);

    map<string, int> freq;
    istringstream iss(line);
    while (iss >> word) freq[word]++;

    for (const auto& [w, c] : freq)
        cout << w << ": " << c << endl;
    return 0;
}

Summary

• map<K,V> stores unique sorted key-value pairs.
• Access: m[key] or m.at(key); search with find() or count().
• Use unordered_map for O(1) average lookups without ordering.