new chnage

languages/C.md

@@ -1,7 +1,48 @@
 <!-- making C cheatsheets -->
 
-main() Function
+```main() Function```
 
 * The main() function is the starting point of the program: ```int main (int argc, char *argv[])```
 * The return type of the main() function is an integer (type int) and it is known as the ```return value``` of the program.
 * As a rule of thumb, ```value 0 means success while non-zero means an error conditions.```
+
+---
+
+## Include Files
+
+* The `purpose` of these files is to tell the compiler about the existence of external functions which the source code will make use of.
+
+---
+
+## Preprocessor directives:
+
+| Directive                   | Description                                        |
+|-----------------------------|----------------------------------------------------|
+| `#include "mine.h"`         | Search current working directory first.           |
+| `#include <stdio.h>`        | Search command line directory, then the system.   |
+| `#define TRUE 1`            | Macro substitution, usually use capitals.         |
+| `#define min(a,b)`          | Macro substitution with parameters.               |
+| `#define abs(a)`            | Macro substitution.                                |
+| `#define note /* comment */` | This comment gets inserted every time `note` appears. |
+| `backslash \ at end of a line` | Means continue the line.                      |
+| `#undef TRUE`               | Undefines a previously defined macro name.       |
+| `#error`                    | Stop compiling at this point.                     |
+| `#if expression`            | Conditional compilation, starts an `if` structure. |
+| `#elif expression`          | Else if expression != 0, compile the following code. |
+| `#else`                     | Else, compile the following code.                 |
+| `#endif`                    | End of conditional compiling.                     |
+| `#ifdef macroname`          | Like `#if`, compiles if `macroname` is defined.   |
+| `#ifndef macroname`         | Like `#if`, compiles if `macroname` is undefined. |
+| `#line number [filename]`   | Set the origin for `__LINE__` and `__FILE__`.    |
+| `#pragma`                   | Gives the compiler commands.                      |
+
+---
+
+## Create and execute a program
+
+In Linux systems: 
+    1. Open up a terminal (Ctrl + Alt + T)
+    2. Create the program: nano nameProgram.c
+    3. Write the program and save it
+    4. gcc -o nameExecutable nameProgram.c  (eg: gcc -o nameProgram_output nameProgram.c
+)