# C
C is a versatile, mature and efficient language.

Expressions are a combination of operators and operands.
An expression followed by a semmicolon (";") is a statement (it is an action)

C concepts
[Memory Management](Memory_Management)
[Structs](Structs)
[Debug messages](Debug_messages)
[Random numbers](/linux/random_numbers)


# Defines
In C you can define stuff that's quickly replaced by the preprocessor.

Let's say you have the following program:

```c
#include <stdio.h>
int main()
{
	printf("Hello, World!\n");
#ifdef DEBUG
	printf("Secret debug info!\n");
#endif
	return 0;
}
```
Compile it with `gcc -o prog -c prog.c -DDEBUG`. Your program will print out the secret debug info in addition to its regular output.
This is useful for debugging and more.


# Storage-class specifiers
Make a variable's storage class more explicit to the compiler.

* static - block scope
Block-scope static variables will keep their values between function calls. They're only initialized once at program startup, unlike regular function variables.

* static - file scope
File-scope static variables (outside of any function) are restricted to the current source file only. You can't access them from another source file.





Notes
-----
* Strings can be literals or arrays. Deep down, they're just pointers to the start of the char array.
	However, string literals are stored read-only and **cannot be modified**: ``char* s;``
	If you want to make a mutable string, declare it as an array of characters: ``char s[];``

* The arrow operator (->) is used to access fields in a pointer to a struct.
	For example: ``thinkpad->price = 800;`` (``thinkpad`` is a pointer to a ``struct laptop thinkpad`` struct)
	This is useful instead of writing it as ``(*thinkpad).price = 800;``

* Include `<stdint.h>` for fixed-size types such as `uint64_t`



See also
--------
https://beej.us/guide/bgc/ -> Great funny introduction to C
https://c-faq.com/index.html -> C FAQs, very useful
https://www.learn-c.org/ -> wip C guide

http://web.archive.org/web/20080217222203/http://c.snippets.org/ Useful public domain C snippets

https://www.andreinc.net/2023/02/01/demystifying-bitwise-ops#number-systems interesting article about binary operators and memory in general

https://verplant.org/oo_programming_in_c.shtml OOP?