address comments

Author: ahans

concepts/headers/about.md

@@ -49,7 +49,8 @@ One possible layout is to keep all the implementation details in the source file
 
 ```cpp
 // A file named robot_flower.h
-#pragma once
+#if !defined(ROBOT_FLOWER_H)
+#define ROBOT_FLOWER_H
 #include <string>
 namespace robots {
     class Flower {

concepts/headers/introduction.md

@@ -49,7 +49,8 @@ One possible layout is to keep all the implementation details in the source file
 
 ```cpp
 // A file named robot_flower.h
-#pragma once
+#if !defined(ROBOT_FLOWER_H)
+#define ROBOT_FLOWER_H
 #include <string>
 namespace robots {
     class Flower {

exercises/concept/doctor-data/.docs/introduction.md

@@ -49,7 +49,8 @@ One possible layout is to keep all the implementation details in the source file
 
 ```cpp
 // A file named robot_flower.h
-#pragma once
+#if !defined(ROBOT_FLOWER_H)
+#define ROBOT_FLOWER_H
 #include <string>
 namespace robots {
     class Flower {

exercises/practice/binary-search/.approaches/introduction.md

@@ -7,14 +7,12 @@ One approach can use a `while` loop with `if` statements.
 
 **binary_search.h**
 ```cpp
-#if !defined(BINARY_SEARCH_H)
-#define BINARY_SEARCH_H
+#pragma once
 #include <vector>
 #include <cstddef>
 namespace binary_search {
     std::size_t find (const std::vector<int>& data, int value);
 }  // namespace binary_search
-#endif // BINARY_SEARCH_H
 ```
 
 **binary_search.cpp**

exercises/practice/binary-search/.approaches/while-with-if-statements/content.md

@@ -3,14 +3,12 @@
 
 **binary_search.h**
 ```cpp
-#if !defined(BINARY_SEARCH_H)
-#define BINARY_SEARCH_H
+#pragma once
 #include <vector>
 #include <cstddef>
 namespace binary_search {
     std::size_t find (const std::vector<int>& data, int value);
 }  // namespace binary_search
-#endif // BINARY_SEARCH_H
 ```
 
 **binary_search.cpp**

exercises/practice/pangram/.approaches/algorithm-allof/content.md

@@ -2,15 +2,12 @@
 
 **pangram.h**
 ```cpp
-#if !defined(PANGRAM_H)
-#define PANGRAM_H
+#pragma once
 #include <string_view>
 
 namespace pangram {
     bool is_pangram(std::string_view phrase);
 }  // namespace pangram
-
-#endif // PANGRAM_H
 ```
 
 **pangram.cpp**

exercises/practice/pangram/.approaches/bitset-all/content.md

@@ -3,15 +3,12 @@
 
 **pangram.h**
 ```cpp
-#if !defined(PANGRAM_H)
-#define PANGRAM_H
+#pragma once
 #include <string_view>
 
 namespace pangram {
     bool is_pangram(std::string_view phrase);
 }  // namespace pangram
-
-#endif // PANGRAM_H
 ```
 
 **pangram.cpp**

exercises/practice/pangram/.approaches/introduction.md

@@ -9,15 +9,12 @@ Another approach can use the [`algorithm.all_of()`][all_of] function.
 
 **pangram.h**
 ```cpp
-#if !defined(PANGRAM_H)
-#define PANGRAM_H
+#pragma once
 #include <string_view>
 
 namespace pangram {
     bool is_pangram(std::string_view phrase);
 }  // namespace pangram
-
-#endif // PANGRAM_H
 ```
 
 **pangram.cpp**

exercises/practice/reverse-string/.approaches/direct-construction/content.md

@@ -2,17 +2,14 @@
 
 **reverse_string.h**
 ```cpp
-#ifndef REVERSE_STRING_H
-#define REVERSE_STRING_H
+#pragma once
 
 #include <string>
 
 namespace reverse_string
 {
     std::string reverse_string(std::string_view str);
 }
-
-#endif // REVERSE_STRING_H
 ```
 
 **reverse_string.cpp**

exercises/practice/reverse-string/.approaches/divide-and-conquer/content.md

@@ -2,17 +2,14 @@
 
 **reverse_string.h**
 ```cpp
-#ifndef REVERSE_STRING_H
-#define REVERSE_STRING_H
+#pragma once
 
 #include <string>
 
 namespace reverse_string
 {
     std::string reverse_string(std::string_view str);
 }
-
-#endif // REVERSE_STRING_H
 ```
 
 **reverse_string.cpp**