cpp: add time duration for std::endl and \n in standard output (#59)

website/docs/cpp/cpp-wiki.md

@@ -45,6 +45,8 @@ int main() {
 
 `std::endl` inserts a newline character (`\n`) into the output stream and flushes the buffer.
 
+### What does `std::endl` do?
+
 The following code examples show the difference between using `std::endl` and not using it.
 
 <Tabs>
@@ -86,6 +88,8 @@ The following code examples show the difference between using `std::endl` and no
 
 </Tabs>
 
+### Standard output vs file output
+
 In standard output, `\n` usually has the same effect as `std::endl`, that is, it inserts a newline character and flushes the buffer. However, in file output, `\n` does not flush the stream, while `std::endl` does.
 
 :::info quote
@@ -187,3 +191,56 @@ To see the difference between `std::endl` and `\n` in file output, run the follo
 
   </TabItem>
 </Tabs>
+
+### Performance
+
+The following example shows the duration for printing 100,000 numbers with `std::endl` and `\n` in standard output.
+
+<Tabs>
+  <TabItem label="Code" value="code">
+
+  ```cpp
+  #include <iostream> // for cin, cout
+  #include <chrono> // for timers
+
+  int endl_each_time(int n = 10000) {
+      const auto start_time = std::chrono::high_resolution_clock::now();
+      for (int i = 0; i < n; i++) {
+          std::cout << i << std::endl;
+      }
+      const auto end_time = std::chrono::high_resolution_clock::now();
+      auto duration_ns = std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time);
+      return duration_ns.count();
+  }
+
+  int new_line_each_time(int n = 10000) {
+      const auto start_time = std::chrono::high_resolution_clock::now();
+      for (int i = 0; i < n; i++) {
+          std::cout << i << "\n";
+      }
+      const auto end_time = std::chrono::high_resolution_clock::now();
+      const auto duration_ns = std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time);
+      return duration_ns.count();
+  }
+
+  int main() {
+      int endl_duration = endl_each_time();
+      int new_line_duration = new_line_each_time();
+      std::cout << "endl_each_time duration: " << endl_duration << "ns" << std::endl;
+      std::cout << "new_line_each_time duration: " << new_line_duration << "ns" << std::endl;
+      return 0;
+  }
+  ```
+
+  </TabItem>
+  <TabItem label="Output" value="output">
+
+  ```shell
+  ...
+  9999
+  endl_each_time duration: 9717ns
+  new_line_each_time duration: 8896ns
+  ```
+
+  </TabItem>
+</Tabs>