awesome-cheatsheets/languages/C.md

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.

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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.

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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.

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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)