C++ Using Find Method in STL Map

Introduction

In this lab, you will learn how to use the find() method in a Map in C++. The find() method is used to search for an element in a Map with a given key. This lab assumes you have basic knowledge of C++ and the Map container.

Create a new C++ file

First, you need to create a new C++ file named main.cpp in the ~/project directory. You can use any text editor or IDE to create and edit this file.

cd ~/project
touch main.cpp

Include necessary libraries and namespace

In the top of the main.cpp file, include the necessary libraries and using directive.

#include <iostream>
#include <map>   //include map library

using namespace std;

Define the main function

Define the main() function to start writing your code.

int main() {
  //Your code
  return 0;   //Exit program
}

Create a Map container

Create a Map container with integer keys and values. The Map container will store key-value pairs sorted in ascending order of keys.

map<int, int> myMap;   //Create a Map container with integer keys and values

Insert elements into the Map

Use the insert() method to insert key-value pairs into the Map container. This step will insert five elements into the Map.

myMap.insert(make_pair(3, 9));
myMap.insert(make_pair(2, 4));
myMap.insert(make_pair(5, 25));
myMap.insert(make_pair(9, 81));
myMap.insert(make_pair(1, 1));

Use the find() method to search for an element

Use the find(x) method to search for an element with key x in the Map. If the element is found, the method returns an iterator to the element. If not found, the method returns an iterator to the end() of the Map container. Here, we will search for elements with keys 5 and 6.

map<int, int>::iterator it;   //Create an iterator for the Map container
it = myMap.find(5);   //Find the element with key 5 in the Map
if (it != myMap.end()) {
  cout << "Element with key 5 is found and the value is " << it->second << endl;
} else {
  cout << "Element with key 5 is not found\n";
}
it = myMap.find(6);   //Find the element with key 6 in the Map
if (it != myMap.end()) {
  cout << "Element with key 6 is found and the value is " << it->second << endl;
} else {
  cout << "Element with key 6 is not found\n";
}

Compile and run the program

Compile the main.cpp file using the following command in the terminal:

g++ main.cpp -o main

Run the program using the following command:

./main

Test the program

After running the program, you should see the following output in the terminal:

Element with key 5 is found and the value is 25
Element with key 6 is not found

This output shows that the element with key 5 is found in the Map and its value is 25. The element with key 6 is not found in the Map.

Complete the code

Copy and paste the following complete code into the main.cpp file.

#include <iostream>
#include <map>

using namespace std;

int main() {
  map<int, int> myMap;   //Create a Map container with integer keys and values
  myMap.insert(make_pair(3, 9));
  myMap.insert(make_pair(2, 4));
  myMap.insert(make_pair(5, 25));
  myMap.insert(make_pair(9, 81));
  myMap.insert(make_pair(1, 1));
  map<int, int>::iterator it;   //Create an iterator for the Map container
  it = myMap.find(5);   //Find the element with key 5 in the Map
  if (it != myMap.end()) {
    cout << "Element with key 5 is found and the value is " << it->second << endl;
  } else {
    cout << "Element with key 5 is not found\n";
  }
  it = myMap.find(6);   //Find the element with key 6 in the Map
  if (it != myMap.end()) {
    cout << "Element with key 6 is found and the value is " << it->second << endl;
  } else {
    cout << "Element with key 6 is not found\n";
  }
  return 0;   //Exit program
}

Summary

Congratulations! You have successfully learned how to use the find() method in a Map container in C++. The find() method is useful for searching for elements with a specific key in a Map container. Remember that the find() method returns an iterator to the element if the element is found, and an iterator to the end() of the Map container if the element is not found.