C++ Maps

C++ Maps: Key-Value Pairs

A Map (often called a dictionary or hash map in other languages) is an incredibly powerful data structure that stores data in Key-Value pairs.

Just like looking up a word in a real dictionary (the Key) to find its definition (the Value), a C++ map lets you associate specific keys with corresponding values.

1. Using a Map

To use a map, include the <map> library.

In a map:

• Every Key must be unique (you can't have two identical keys).
• The Values can be duplicated.
• A standard map sorts the data automatically based on the Keys.

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

int main() {
  // Create a map where the Key is a string, and Value is an integer
  map<string, int> userAges;
  // Assigning values to keys using the [] operator
  userAges["Alice"] = 25;
  userAges["Bob"] = 30;
  userAges["Charlie"] = 22;
  // Accessing a value using a key
  cout << "Bob's age is: " << userAges["Bob"] << "\n";
  // Updating an existing value
  userAges["Alice"] = 26; 
  cout << "Alice's updated age is: " << userAges["Alice"] << "\n";
  return 0;
}

2. Iterating Through a Map

To loop through a map, you need to understand that each item is a pair. You can access the key using .first and the value using .second.

for (auto item : userAges) {
  cout << item.first << " is " << item.second << " years old.\n";
}