Range-Based For Loop with a Map in C++

In C++, a map is a container that stores elements formed by a combination of a key value and a mapped value. A range-based for loop is a feature added in C++11 to iterate over containers. In this article, we will learn how to use a range-based for loop with a map in C++.

Example:

Input:
myMap: { {1, “John”}, {2, “Adam”} }

Output:
1: John
2: Adam

Range-Based for Loop with a Map in C++

We can use the range-based for loop with a std::map to replace any other loop and simplify the code. The range-based for loop will take the name of the map and iterator over each element in the container.

C++ Program to Traverse Map with Range Based for Loop

C++

// C++ Program to Use a Range-Based For Loop with a Map
#include <iostream>
#include <map>
using namespace std;

// Driver Code
int main()
{
    // Decalarion and intitalization of the map with key of
    // type string and value of type int
    map<string, int> priceOfFruits = { { "Apple", 50 },
                                       { "Mango", 30 },
                                       { "Banana", 25 },
                                       { "Orange", 20 } };

    // Printing the key and values of the map
    cout << "Ranged-based for loop with read-only iterator"
         << endl;
    for (const auto eachPair : priceOfFruits) {
        cout << eachPair.first << ": " << eachPair.second
             << endl;
    }

    // Modifying the values of the map and then printing the
    // key and values of the map
    cout << "Ranged-based for loop with writable iterator"
         << endl;
    for (auto& eachPair : priceOfFruits) {
        eachPair.second += 10;
        cout << eachPair.first << ": " << eachPair.second
             << endl;
    }

    return 0;
}

Output

Ranged-based for loop with read-only iterator
Apple: 50
Banana: 25
Mango: 30
Orange: 20
Ranged-based for loop with writable iterator
Apple: 60
Banana: 35
Mango: 40
Orange: 30

Time Complextiy: O(N logN), where N is the number of elements.
Space Complexity: O(1)