<div class="image-550">
<img src="https://cdn.kahimyang.com/resources-24/stl-parallel.avif" alt="Sequential and Parallel Algorithms" loading="lazy" />
</div>
<p>
In this article, we'll explore STL algorithms with and without parallel execution, discuss the need for synchronization, and provide examples to demonstrate their usage.
</p>
<h3>
Overview of STL Algorithms
</h3>

<p>
STL algorithms are functions that operate on ranges of elements, typically defined by iterators. They are categorized into several types, including:
</p>
<ol style="margin-left: -15px">
<li>
Sorting and Searching: <b>std::sort</b>, <b>std::binary_search</b>
</li>
<li>
Modifying Operations: <b>std::transform</b>, <b>std::fill</b>
</li>
<li>
Non-Modifying Operations: <b>std::for_each</b>, <b>std::count</b>
</li>
<li>
Numeric Operations: <b>std::accumulate</b>, <b>std::inner_product</b>
</li>
</ol>
<p>
These algorithms are part of the <b>&lt;algorithm></b> and <b>&lt;numeric></b> headers and can be applied to containers like <b>std::vector</b>, <b>std::list</b>, and <b>std::array</b>.
</p>

<h3>
Sequential Execution of STL Algorithms
</h3>
<p>
By default, STL algorithms execute sequentially, processing elements one at a time. This is suitable for small datasets or when parallel execution is unnecessary.
</p>
<h4>
Example: Sequential std::transform
</h4>
<pre style="font-size: 90%;">
<code class="language-cpp normalize-whitespace line-numbers" >
#include &lt;iostream>
#include &lt;vector>
#include &lt;algorithm> // for std::transform

int main() {
    std::vector&lt;int> vec = {1, 2, 3, 4, 5};
    std::vector&lt;int> result(vec.size());

    // Multiply each element by 2
    std::transform(vec.begin(), vec.end(), result.begin(), 
                        [](int x) {
        return x * 2;
    });

    // Print the transformed vector
    std::cout &lt;&lt; "Transformed vector: ";
    for (int num : result) {
        std::cout &lt;&lt; num &lt;&lt; " ";
    }
    std::cout &lt;&lt; std::endl;

    return 0;
}
</code>
</pre>
<p>
<b>
Output:
</b>
</p>
<pre style="font-size: 90%;">
<code class="language-text normalize-whitespace line-numbers" >
Transformed vector: 2 4 6 8 10
</code>
</pre>


Parallel STL Algorithms in C++: Explicit Synchronization