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:

C++
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1#include <iostream>
2#include <vector>
3#include <algorithm>
4
5int main() {
6    std::vector<int> data = {1, 2, 3, 4, 5, 6};
7
8    // Check if any elements are greater than 4
9    bool any_greater_than_4 = std::any_of(data.begin(), data.end(), [](int n) {
10        return n > 4;
11    });
12
13    std::cout << "Any number greater than 4: " << (any_greater_than_4 ? "Yes" : "No") << '\n'; // Output: Any number greater than 4: Yes
14
15    return 0;
16}

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:

C++
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1#include <iostream>
2#include <vector>
3#include <algorithm>
4
5int main() {
6    std::vector<int> data = {2, 4, 6, 8, 10};
7
8    // Check if all elements are even
9    bool all_even = std::all_of(data.begin(), data.end(), [](int n) {
10        return n % 2 == 0;
11    });
12
13    std::cout << "All numbers are even: " << (all_even ? "Yes" : "No") << '\n'; // Output: All numbers are even: Yes
14
15    return 0;
16}

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.

Finally, let’s look at std::none_of, which checks if no elements in a range satisfy a condition:

C++
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1#include <iostream>
2#include <vector>
3#include <algorithm>
4
5int main() {
6    std::vector<int> data = {1, 3, 5, 7};
7
8    // Check if no element is negative
9    bool none_negative = std::none_of(data.begin(), data.end(), [](int n) {
10        return n < 0;
11    });
12
13    std::cout << "No negative number: " << (none_negative ? "Yes" : "No") << '\n'; // Output: No negative number: Yes
14
15    return 0;
16}

In this example, we use std::none_of and the lambda function (int n) { return n < 0; } to verify that no elements in the vector data are negative. If none of the elements meet the condition, std::none_of returns true.

We covered three essential Boolean functions in C++: std::any_of, std::all_of, and std::none_of. These functions allow you to efficiently check conditions across collections:

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

Understanding and using these functions lets you write cleaner and more expressive C++ code.

Now that you've grasped the theory and seen examples of Boolean functions in action, it's time to put your knowledge to the test. In the next section, you'll engage in hands-on practice to reinforce these concepts. Ready to dive in? Let's get started!