New Entry C & C++ Macros

content/c/concepts/macros/macros.md

@@ -0,0 +1,147 @@
+---
+Title: 'Macros'
+Description: 'A macro is a label defined in the source code that is replaced by its value by the preprocessor before compilation.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Command Line'
+  - 'Developer Tools'
+CatalogContent:
+  - 'learn-c'
+  - 'paths/computer-science'
+---
+
+A **macro** is a label defined in the source code that is replaced by its value by the [preprocessor](https://www.codecademy.com/resources/docs/c/preprocessors) before [compilation](https://www.codecademy.com/resources/docs/c/compiling). Macros are initialized with the `#define` preprocessor command and can be undefined with the `#undef` command.
+
+There are two types of macros: object-like macros and function-like macros.
+
+## Object-Like Macros
+
+These macros are replaced by their value in the source code before compilation. Their primary purpose is to define constants to be used in the code.
+
+**Note**: Macro definitions are not followed by a semicolon `;`.
+
+### Example
+
+In the following example, `PI` is defined as an object-like macro:
+
+```c
+#include <stdio.h>
+#define PI 3.1416
+
+int main() {
+  float radius = 3;
+  float area;
+  area = PI * radius * radius;
+  printf("Area is: %f",area);
+  return 0;
+}
+```
+
+This example outputs the following:
+
+```shell
+Area is: 28.274401
+```
+
+## Function-Like Macros
+
+These macros behave like [functions](https://www.codecademy.com/resources/docs/c/functions), in that they take arguments that are used in the replaced code. Note that in defining a function-like macro, there cannot be a space between the macro name and the opening parenthesis.
+
+### Example
+
+In the following example, `AREA` is defined as a function-like macro. Note that other macros can be used in defining a subsequent macro. The inner macro is replaced by its value before the outer macro is replaced.
+
+```c
+#include <stdio.h>
+#define PI 3.1416
+#define AREA(r) r * r * PI
+
+int main() {
+  float radius = 5;
+  float result;
+  result = AREA(radius);
+  printf("Area is: %f",result);
+  return 0;
+}
+```
+
+This example outputs the following:
+
+```shell
+Area is: 78.540001
+```
+
+## Predefined Macros
+
+C has a number of predefined macros, including the following:
+
+- `__DATE__`: Current date formatted as `MMM DD YYYY`.
+- `__TIME__`: Current time formatted as `HH:MM:SS`.
+- `__FILE__`: Current filename.
+- `__LINE__`: Current line number.
+
+### Example
+
+The following example uses the above predefined macros:
+
+```c
+#include <stdio.h>
+int main() {
+
+char file[] = __FILE__;
+char date[] = __DATE__;
+char time[] = __TIME__;
+int line = __LINE__;
+
+printf("File name: %s\n", file);
+printf("Date: %s\n", date);
+printf("Time: %s\n", time);
+printf("Line number: %d\n", line);
+}
+```
+
+The output resembles the following:
+
+```shell
+File name: main.c
+Date: Jun 25 2022
+Time: 14:05:33
+Line number: 7
+```
+
+## Undefining a Macro
+
+Once defined, a macro can be undefined with the `#undef` command. Using the macro after that point will result in a compile error.
+
+### Example
+
+```c
+#include <stdio.h>
+#define TEST 1
+
+int main() {
+  #ifdef TEST
+    printf("TEST defined\n");
+  #else
+    printf("TEST undefined\n");
+  #endif
+
+  #undef TEST
+
+  #ifdef TEST
+    printf("TEST defined\n");
+  #else
+    printf("TEST undefined\n");
+  #endif
+
+}
+```
+
+This results in the output:
+
+```shell
+TEST defined
+TEST undefined
+```

content/c/concepts/preprocessors/preprocessors.md

@@ -63,7 +63,7 @@ The example above will compile different code for different operating systems ba
 
 ### Defining Macros
 
-When the preprocessor encounters a macro in the source code, it will replace the macro with the value it has been assigned. Macros are defined by using `#define` and can be undefined using `#undef`.
+When the preprocessor encounters a [macro](https://www.codecademy.com/resources/docs/c/macros) in the source code, it will replace the macro with the value it has been assigned. Macros are defined by using `#define` and can be undefined using `#undef`.
 
 ```c
 #define PI 3.1416

content/cpp/concepts/macros/macros.md

@@ -0,0 +1,157 @@
+---
+Title: 'Macros'
+Description: 'A macro is a label defined in the source code that is replaced by its value by the preprocessor before compilation.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Command Line'
+  - 'Developer Tools'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+A **macro** is a label defined in the source code that is replaced by its value by the preprocessor before compilation. Macros are initialized with the `#define` preprocessor command and can be undefined with the `#undef` command.
+
+There are two types of macros: [object](https://www.codecademy.com/resources/docs/cpp/objects)-like macros and [function](https://www.codecademy.com/resources/docs/cpp/functions)-like macros.
+
+## Object-Like Macros
+
+These macros are replaced by their value in the source code before compilation. Their primary purpose is to define constants to be used in the code.
+
+**Note**: Macro definitions are not followed by a semicolon `;`.
+
+### Example
+
+In the following example, `PI` is defined as an object-like macro:
+
+```cpp
+#include <iostream>
+using namespace std;
+
+#define PI 3.1416
+
+int main() {
+  float radius = 3;
+  float area;
+  area = PI * radius * radius;
+  cout << "Area is " << area;
+  return 0;
+}
+```
+
+This example outputs the following:
+
+```shell
+Area is 28.2744
+```
+
+## Function-Like Macros
+
+These macros behave like functions, in that they take arguments that are used in the replaced code.
+
+**Note**: When defining a function-like macro, there cannot be a space between the macro name and the opening parenthesis.
+
+### Example
+
+In the following example, `AREA` is defined as a function-like macro. Note that other macros can be used in defining a subsequent macro. The inner macro is replaced by its value before the outer macro is replaced.
+
+```cpp
+#include <iostream>
+using namespace std;
+
+#define PI 3.1416
+#define AREA(r) r * r * PI
+
+int main() {
+  float radius = 5;
+  float result;
+  result = AREA(radius);
+  cout << "Area is " << result;
+  return 0;
+}
+```
+
+This example outputs the following:
+
+```shell
+Area is 78.54
+```
+
+## Predefined Macros
+
+C++ has a number of predefined macros, including the following:
+
+- `__DATE__`: Current date formatted as `MMM DD YYYY`.
+- `__TIME__`: Current time formatted as `HH:MM:SS`.
+- `__FILE__`: Current filename.
+- `__LINE__`: Current line number.
+
+### Example
+
+The following example uses the predefined macros mentioned above:
+
+```cpp
+#include <iostream>
+using namespace std;
+
+int main() {
+
+char file[] = __FILE__;
+char date[] = __DATE__;
+char time[] = __TIME__;
+int line = __LINE__;
+
+cout << "File name: " << file << "\n";
+cout << "Date: " << date << "\n";
+cout << "Time: " << time << "\n";
+cout << "Line number: " << line << "\n";
+}
+```
+
+The output resembles the following:
+
+```shell
+File name: main.cpp
+Date: Jun 25 2022
+Time: 14:17:50
+Line number: 9
+```
+
+## Undefining a Macro
+
+Once defined, a macro can be undefined with the `#undef` command. Using the macro after that point will result in a compile error.
+
+### Example
+
+```cpp
+#include <iostream>
+using namespace std;
+
+#define TEST 1
+
+int main() {
+  #ifdef TEST
+    cout << "TEST defined\n";
+  #else
+    cout << "TEST undefined\n";
+  #endif
+
+  #undef TEST
+
+  #ifdef TEST
+    cout << "TEST defined\n";
+  #else
+    cout << "TEST undefined\n";
+  #endif
+
+}
+```
+
+This results in the output:
+
+```shell
+TEST defined
+TEST undefined
+```