[C++] added 3 snippets for string.

Author: majvax

snippets/cpp/string-manipulation/filter.md

@@ -0,0 +1,18 @@
+---
+title: Filter
+description: Filter a string with a predicate function
+author: majvax
+tags: cpp,string,utility,filtering
+---
+
+```cpp
+#include <ranges>
+#include <string>
+
+template <typename P>
+std::string filter(const std::string& str, P&& predicate) {
+    return str
+        | std::ranges::views::filter(std::forward<P>(predicate))
+        | std::ranges::to<std::string>();
+}
+```

snippets/cpp/string-manipulation/palindrome.md

@@ -0,0 +1,21 @@
+---
+title: Palindrome
+description: Check if a string is a palindrome or not.
+author: majvax
+tags: cpp,string,utility
+---
+
+```cpp
+#include <string>
+#include <ranges>
+#include <algorithm>
+
+bool is_palindrome(const std::string& str) {
+    std::string sanitized_string = str
+        | std::ranges::views::filter([](char c){ return std::isalnum(c); })
+        | std::ranges::views::transform([](char c){ return std::tolower(c); })
+        | std::ranges::to<std::string>();
+    
+    return std::ranges::equal(sanitized_string, sanitized_string | std::views::reverse);
+}
+```

snippets/cpp/string-manipulation/transform.md

@@ -0,0 +1,18 @@
+---
+title: Transform
+description: Transform a string with a function
+author: majvax
+tags: cpp,string,utility,transform
+---
+
+```cpp
+#include <ranges>
+#include <string>
+
+template <typename F>
+std::string transform(const std::string& str, F&& transformer) {
+    return str
+        | std::ranges::views::transform(std::forward<F>(transformer))
+        | std::ranges::to<std::string>();
+}
+```