Boolean Functions in C++

In this lesson, we explore an important aspect of functional programming in C++: Boolean functions. Boolean functions are essential for making decisions in code. Our goal is to understand how to use std::any_of, std::all_of, and std::none_of in C++ to perform checks across collections.

By the end of this lesson, you'll be able to efficiently check if any, all, or none of the elements in a container meet specific criteria. Let’s dive in!

Boolean functions in the STL help perform checks across collections, making code more expressive and concise. The three key Boolean functions are:

• std::any_of: Checks if any elements in a range match a condition.
• std::all_of: Checks if all elements in a range match a condition.
• std::none_of: Checks if none of the elements in a range match a condition.

These functions are useful for making decisions based on the properties of container elements.

Let's begin with std::any_of, which checks if any elements in a range satisfy a condition. Here is an example:

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> data = {1, 2, 3, 4, 5, 6};

    // Check if any elements are greater than 4
    bool any_greater_than_4 = std::any_of(data.begin(), data.end(), [](int n) {
        return n > 4;
    });

    std::cout << "Any number greater than 4: " << (any_greater_than_4 ? "Yes" : "No") << '\n'; // Output: Any number greater than 4: Yes

    return 0;
}

Here, we use std::any_of to check if any numbers in the vector are greater than 4. The lambda function (int n) { return n > 4; } defines the condition. If any element meets the condition, std::any_of returns true.

Next, let’s explore std::all_of. This function checks if all elements in a range meet a condition. Here’s how it works:

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> data = {2, 4, 6, 8, 10};

    // Check if all elements are even
    bool all_even = std::all_of(data.begin(), data.end(), [](int n) {
        return n % 2 == 0;
    });

    std::cout << "All numbers are even: " << (all_even ? "Yes" : "No") << '\n'; // Output: All numbers are even: Yes

    return 0;
}

Here, std::all_of checks if all elements in the vector data are even. We use the lambda function (int n) { return n % 2 == 0; } for the condition. If all elements satisfy the condition, std::all_of returns true.