wiki: avoid using namespace std; in C++ (#53)

website/docs/cpp/cpp-wiki.md

@@ -0,0 +1,31 @@
+---
+title: "C++"
+description: "A collection of useful C++ usage and tips."
+---
+
+## Avoid `using namespace std;`
+
+It is common to encounter `using namespace std;` in various C++ sample codes, as it negates the need to prefix `std::` before each standard library object. However, it is not recommended to use it in your code. The reason is that `using namespace std;` might cause name conflicts.
+
+Consider a scenario where you have a function or variable named `max`. If you declare `using namespace std;`, then you will get an error when you try to use `max` because it conflicts with `std::max`.
+
+```cpp
+#include <iostream>
+using namespace std;
+
+int max = 0;
+int main() {
+    cout << max << endl; // error: reference to 'max' is ambiguous
+}
+```
+
+To avoid the preceding error, use the following code instead:
+
+```cpp
+#include <iostream>
+
+int max = 0;
+int main() {
+    std::cout << max << std::endl; // 0
+}
+```

website/sidebars.js

@@ -45,6 +45,16 @@ const sidebars = {
       ],
     },
     'git-wiki',
+    {
+      type: 'category',
+      label: 'C++',
+      link: {
+        type: 'generated-index',
+      },
+      items: [
+        'cpp/cpp-wiki'
+      ],
+    },
     {
       type: 'category',
       label: 'Python',