How to Check if a Value Exists in a Map in C++ - Step by Step Examples

How to Check if a Value Exists in a Map in C++ ?

Answer

To check if a value exists in a map in C++, you can use a loop to iterate through the map and compare each value. This approach helps determine if a specific value is present in the map.

✐ Examples

1 Checking if a Value Exists Using Loop

We can check if a value exists in a map in C++ using a loop to iterate through the map and compare each value to the specified value.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We declare a boolean variable valueExists and initialize it to false. This variable will be used to indicate if the value is found in the map.
We use a range-based for loop to iterate through each key-value pair in the map. Inside the loop, we compare the value of the current pair with the specified value.
If the value matches the specified value, we set valueExists to true and break the loop.
We print the result to the console using std::cout.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, std::string> myMap = {
        {1, "one"},
        {2, "two"},
        {3, "three"}
    };

    // Check if a value exists using loop
    bool valueExists = false;
    for (const auto& pair : myMap) {
        if (pair.second == "two") {
            valueExists = true;
            break;
        }
    }

    // Print the result
    std::cout << "Does value 'two' exist? " << (valueExists ? "Yes" : "No") << std::endl;

    return 0;
}

Output

Does value 'two' exist? Yes

2 Checking if a Value Does Not Exist Using Loop

We can check if a value does not exist in a map in C++ using a loop to iterate through the map and compare each value to the specified value.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We declare a boolean variable valueExists and initialize it to false. This variable will be used to indicate if the value is found in the map.
We use a range-based for loop to iterate through each key-value pair in the map. Inside the loop, we compare the value of the current pair with the specified value.
If the value matches the specified value, we set valueExists to true and break the loop.
We print the result to the console using std::cout.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, std::string> myMap = {
        {1, "one"},
        {2, "two"},
        {3, "three"}
    };

    // Check if a value does not exist using loop
    bool valueExists = false;
    for (const auto& pair : myMap) {
        if (pair.second == "four") {
            valueExists = true;
            break;
        }
    }

    // Print the result
    std::cout << "Does value 'four' exist? " << (valueExists ? "Yes" : "No") << std::endl;

    return 0;
}

Output

Does value 'four' exist? No

3 Checking Multiple Values Using Loop

We can check if multiple values exist in a map in C++ using a loop to iterate through the map and compare each value to the specified values.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We declare two boolean variables valueExistsOne and valueExistsFour, and initialize them to false. These variables will be used to indicate if the values are found in the map.
We use a range-based for loop to iterate through each key-value pair in the map. Inside the loop, we compare the value of the current pair with the specified values.
If the value matches one of the specified values, we set the corresponding boolean variable to true and break the loop.
We print the results to the console using std::cout.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, std::string> myMap = {
        {1, "one"},
        {2, "two"},
        {3, "three"}
    };

    // Check if multiple values exist using loop
    bool valueExistsOne = false;
    bool valueExistsFour = false;
    for (const auto& pair : myMap) {
        if (pair.second == "one") {
            valueExistsOne = true;
        }
        if (pair.second == "four") {
            valueExistsFour = true;
        }
    }

    // Print the results
    std::cout << "Does value 'one' exist? " << (valueExistsOne ? "Yes" : "No") << std::endl;
    std::cout << "Does value 'four' exist? " << (valueExistsFour ? "Yes" : "No") << std::endl;

    return 0;
}

Output

Does value 'one' exist? Yes
Does value 'four' exist? No

Summary

In this tutorial, we learned How to Check if a Value Exists in a Map in C++ language with well detailed examples.

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How to Check if a Value Exists in a Map in C++ - Step by Step Examples