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Connor
2019-02-20 04:24:41 +00:00
committed by Manish Giri
parent 551c97feb1
commit 2424f7892b
1 changed files with 5 additions and 4 deletions
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guide/english/c/macros/index.md
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@ -3,7 +3,9 @@ title: Macros in C
--- ---
## Macros in C ## Macros in C
A macro is a piece of code with a given name. When the name is used, it is replaced by the content of the macro. The `#define` keyword is used to define new macros. It's followed by a name and a content. By convention, macro names are written in uppercase. There are two type of macros: `Object-like` macros and `Function-like` macros. A macro is a piece of code with a given name. When the name is used, it is replaced by the content of the macro. This is handled by the C Preprocessor, before compilation.
The `#define` keyword is used to define new macros. It's followed by a name and a content. By convention, macro names are written in uppercase. There are two type of macros: `Object-like` macros and `Function-like` macros.
#### Why Macros? #### Why Macros?
The C compiler will go through your code and replace every occurrence of a macro with it's value. This begs the question, what is the point of using macros? The answer: macros are a tool for the programmer, not for the program. The C compiler will go through your code and replace every occurrence of a macro with it's value. This begs the question, what is the point of using macros? The answer: macros are a tool for the programmer, not for the program.
@ -12,9 +14,8 @@ If you have the number `365` hard-coded into your program, it becomes difficult
It's also beneficial if you have many instances of the same thing. If you'd used `2018` as the year in multiple places in your program, and then the year changed to `2019`, you would have to go and find every single line containing `2018` and change it, hoping you didn't miss any. With the macro `#define YEAR 2018`, you can simply change the value of the macro and be confident all of the values have been updated accordingly. It's also beneficial if you have many instances of the same thing. If you'd used `2018` as the year in multiple places in your program, and then the year changed to `2019`, you would have to go and find every single line containing `2018` and change it, hoping you didn't miss any. With the macro `#define YEAR 2018`, you can simply change the value of the macro and be confident all of the values have been updated accordingly.
#### Defining macros #### Defining macros
The `#define` keyword is used to define new macros. It's followed by a name and a content, but no equals sign. By convention, macro names are written in uppercase. The `#define` keyword is used to define new macros. It's followed by a name and the replacement code, but no equals sign. By convention, macro names are written in uppercase.
```C ```C
#define PI 3.14 #define PI 3.14
@ -24,7 +25,7 @@ If you use the macro this way:
```C ```C
printf("Value of PI: %d", PI); printf("Value of PI: %d", PI);
``` ```
Is the same as write this: Is the same as writing this:
```C ```C
printf("Value of PI: %d", 3.14); printf("Value of PI: %d", 3.14);
``` ```