Lära Non-modifying Algorithms

Non-modifying algorithms in the C++ Standard Library allow you to analyze or search through containers without changing their contents. These algorithms are essential for querying data, checking conditions, or finding elements while guaranteeing that the underlying container remains unaltered.

Some of the most commonly used non-modifying algorithms include std::find, std::count, std::all_of, and std::any_of:

You can apply these algorithms to a wide range of containers, such as std::vector, std::list, or std::set. For instance, std::find locates a specific element, while std::count counts occurrences of a value. Algorithms like std::all_of and std::any_of are ideal for validation and filtering tasks, allowing you to efficiently check conditions across an entire container while ensuring the underlying data remains unchanged.

main.cpp


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

int main()
{
    std::vector<int> numbers{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    // Using std::find to locate the value 5
    auto it = std::find(numbers.begin(), numbers.end(), 5);
    
    if (it != numbers.end())
        std::cout << "Found 5 at position: " << std::distance(numbers.begin(), it) << '\n';
    else
        std::cout << "5 not found\n";

    // Using std::count_if to count even numbers
    int even_count = std::count_if(numbers.begin(), numbers.end(), [](int n) { return n % 2 == 0; });
    std::cout << "Number of even elements: " << even_count << '\n';
}

Many non-modifying algorithms, such as std::count_if, std::all_of, and std::any_of, accept predicate functions as arguments. A predicate function is a callable object such as a function, lambda, or functor that takes an element from the container and returns a boolean value indicating whether the element satisfies a certain condition.

Use a lambda expression as a predicate to count all numbers greater than a specific value;
Check if all elements in a std::vector are positive;
Validate or filter elements without writing explicit loops.

Note

Predicate functions are a powerful way to extend the utility of STL algorithms without modifying your container or introducing manual iteration.

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