C.txt

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:
  #include "mine.h"	search current working directory first
  #include <stdio.h>	search command line directory then system
  #define TRUE 1	macro substitution, usually use capitals
  #define min(a,b) (a<b)?(a):(b)	macro substitution with parameters
  #define abs(a) (a<0)?(-(a)):(a)	macro substitution
  #define note /* comment */	this comment gets inserted every time note appears */
  backslash \ at end of a line means continue
  #undef TRUE	undefines a previously defined macroname
  #error	stop compiling at this point
  #if expression	conditional compilation, start if structure
  #elif expression	else if expression != 0 compile following code
  #else	else compile following code
  #endif	end of conditional compiling
  #ifdef macroname	like #if, compiles if macroname defined
  #ifndef	like #if, compiles if macroname undefined
  #line number [filename]	set origin for __LINE__ and __FILE__
  #pragma	gives the compiler commands

Create and execute a program

In Linux systems: 
    1. Open up a terminal
    2. Create the program: nano nameProgram.c
    3. Write the program and save it
    4. gcc -o nameExecutable nameProgram.c 

32 Reserved words

Term	    Description
auto	    optional local declaration
break 	  used to exit loop and used to exit switch
case	    choice in a switch
char	     basic declaration of a type character
const	     prefix declaration meaning variable can not be changed
continue 	go to bottom of loop in for, while and do loops
default	   optional last case of a switch
do	       executable statement, do-while loop
double     basic declaration double precision floating point
else	    executable statement, part of "if" structure
enum	    basic declaration of enumeration type
extern	  prefix declaration meaning variable is defined externally
float	    basic declaration of floating point
for	      executable statement, for loop
goto	    jump within function to a label
if	      executable statement
int	      basic declaration of integer
long	    prefix declaration applying to many types
register	prefix declaration meaning keep variable in register
return	  executable statement with or without a value
short	    prefix declaration applying to many types
signed	  prefix declaration applying to some types
sizeof	  operator applying to variables and types, gives size in bytes
static	  prefix declaration to make local variable static
struct	  declaration of a structure, like a record
switch	  executable statement for cases
typedef	  creates a new type name for an existing type
union	    declaration of variables that are in the same memory locations
unsigned	prefix declaration applying to some types
void	    declaration of a typeless variable
volatile	prefix declaration meaning the variable can be changed at any time
while	    executable statement, while loop or do-while loop

Basic types

Type	    Description
char	    character type, usually one byte ( a string is array of char )
int	      integer type, usually 2 or 4 bytes ( default )
float	    floating point type, usually 4 bytes
double	  floating point type, usually 8 bytes
void	    no type, typeless
enum	    enumeration type ( user defines the type name )

Type modifiers, prefix for basic types

Modifiers	  Description
signed	    has a sign ( default )
unsigned	  no sign bit in variable
long	      longer version of type (short or long alone means short int or
short	      shorter version of type long int because int is the default)
const	       variable can not be stored into


Storage Types

Prefix	   Description
auto	     local variable ( default )
static	   permanent when function exits, not auto
volatile   can change from outside influence
extern	   variables are defined elsewhere, externally
register   assign variable to register

Operators

  ( )	  grouping parenthesis, function call
  [ ]	  array indexing, also  [ ][ ]  etc.
  ->   	selector, structure pointer  
  .	    select structure element     
  !	    relational not, complement, ! a  yields true or false
  ~    	bitwise not, ones complement, ~ a
  ++  	increment, pre or post to a variable
  --   	decrement, pre or post to a variable
  -   	unary minus, - a
  +    	unary plus,  + a
  *    	indirect, the value of a pointer,  * p is value at pointer p address
  &    	the memory address, & b is the memory address of variable b
  sizeof size in bytes,   sizeof a     or  sizeof (int)
	(type) a cast, explicit type conversion,  (float) i, (*fun)(a,b), (int*)x
  *   	multiply, a * b
  /   	divide, a / b
  %    	modulo, a % b
  +    	add, a + b
  -    	subtract, a - b
  <<   	shift left,  left operand is shifted left by right operand bits
  >>   	shift right, left operand is shifted right by right operand bits
  <    	less than, result is true or false,  a %lt; b
  <=   	less than or equal, result is true or false,  a <= b
  >    	greater than, result is true or false,  a > b
  >=   	greater than or equal, result is true or false, a >= b
  ==   	equal, result is true or false,  a == b
  !=   	not equal, result is true or false,  a != b
  &    	bitwise and,  a & b
  ^   	bitwise exclusive or,  a ^ b
  |    	bitwise or,  a | b
  &&  	relational and, result is true or false,  a < b && c >= d
  ||	  relational or, result is true or false,  a < b || c >= d
  ?    	exp1 ? exp2 : exp3  result is exp2 if exp1 != 0, else result is exp3
  =    	store
  +=   	add and store
  -=   	subtract and store
  *=   	multiply and store
  /=  	divide and store
  %= 	  modulo and store
  <<=  	shift left and store
  >>=  	shift right and store
  &=   	bitwise and and store
  ^=   	bitwise exclusive or and store
  |=   	bitwise or and store
  ,    	separator as in   ( y=x,z=++x )
  ;     statement terminator.


Operator precedence
                
More precedence

LR	( ) [ ] -> . x++ x--
RL	! ~ - + ++x --x * & sizeof (type)
LR	* / %
LR	+ -
LR	<< >>
LR	< <= > >=
LR	== !=
LR	&
LR	^
LR	|
LR	&&
LR	||
RL	? :
RL	= += -= *= /= %= >>= <<= &= ^= |=
LR	,

Less precedence

Conditional branching

 if ( condition ) statement ;
  else statement_2 ;            /* optional  else  clause */

Switch statement

switch ( expression )      /* constants must be unique              */
  {
      case constant_1:       /* do nothing for this case              */
         break;
      case constant_2:       /* drop through and do same as constant_3*/
      case constant_3:
         statement_sequence  /* can have but does not need  { }       */
         break;
      case constant_4:
         statement_sequence  /* does this and next */
                            		 /* statement_sequence also*/
      case constant_5:
         statement_sequence
         break;
      default:               /* default executes if no constant equals*/
         statement_sequence  /* the expression. This is optional      */
 }

Function definition

type function_name(int a, float b, const char * ch,...) { function_body }

/* only parameters passed by address can are modified*/ 

/* in the calling function, local copy can be modified*/

char * strcpy( char * s1, const char * s2 ) { statements }

Declarations forms

basic_type variable;

type variable[val][val]...[val]={data,data,...};  /*multidimensional array*/

struct struct_name {     /* struct_name is optional */
     type variable_1;    /* any declaration */
     …                   /* all variable names must be unique*/
} variable_1, ... ;      /* variables are optional */

struct struct_name {          /* struct_name is optional */
     type variable_1: length; /* any declaration : length in bits */
         ...					        /* type is int, unsigned or signed */
} variable_1, ... ;           /* variables are optional, they can also be arrays and pointers */


union union_name {            /* union_name is optional */
    type variable_1;          /* variable_1 overlays variable_2 */
    type variable_2;
        ...
} variable_a, ...;            /* variables are optional */

enum enum_type                /* enum_name is optional */
  { enumeration_name_1,       /* establishes enumeration literals */
    enumeration_name_2=number,/* optional number, */
      ...                     /* default is 0, 1, 2, ... */
  } variable, ...;            /* variables are optional */

 /* use dot notation to select a component of a struct or union */