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Create C.txt
Brief summary of C
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languages/C.txt
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241
languages/C.txt
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main() Function
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* The main() function is the starting point of the program: int main (int argc, char *argv[])
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* The return type of the main() function is an integer (type int) and it is known as the return value of the program.
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* As a rule of thumb, value 0 means success while non-zero means an error conditions.
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Include Files
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* 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:
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#include "mine.h" search current working directory first
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#include <stdio.h> search command line directory then system
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#define TRUE 1 macro substitution, usually use capitals
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#define min(a,b) (a<b)?(a):(b) macro substitution with parameters
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#define abs(a) (a<0)?(-(a)):(a) macro substitution
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#define note /* comment */ this comment gets inserted every time note appears */
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backslash \ at end of a line means continue
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#undef TRUE undefines a previously defined macroname
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#error stop compiling at this point
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#if expression conditional compilation, start if structure
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#elif expression else if expression != 0 compile following code
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#else else compile following code
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#endif end of conditional compiling
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#ifdef macroname like #if, compiles if macroname defined
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#ifndef like #if, compiles if macroname undefined
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#line number [filename] set origin for __LINE__ and __FILE__
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#pragma gives the compiler commands
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Create and execute a program
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In Linux systems:
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1. Open up a terminal
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2. Create the program: nano nameProgram.c
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3. Write the program and save it
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4. gcc -o nameExecutable nameProgram.c
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32 Reserved words
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Term Description
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auto optional local declaration
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break used to exit loop and used to exit switch
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case choice in a switch
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char basic declaration of a type character
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const prefix declaration meaning variable can not be changed
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continuego to bottom of loop in for, while and do loops
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default optional last case of a switch
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do executable statement, do-while loop
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double basic declaration double precision floating point
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else executable statement, part of "if" structure
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enum basic declaration of enumeration type
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extern prefix declaration meaning variable is defined externally
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float basic declaration of floating point
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for executable statement, for loop
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goto jump within function to a label
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if executable statement
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int basic declaration of integer
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long prefix declaration applying to many types
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register prefix declaration meaning keep variable in register
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return executable statement with or without a value
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short prefix declaration applying to many types
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signed prefix declaration applying to some types
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sizeof operator applying to variables and types, gives size in bytes
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static prefix declaration to make local variable static
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struct declaration of a structure, like a record
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switch executable statement for cases
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typedef creates a new type name for an existing type
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union declaration of variables that are in the same memory locations
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unsigned prefix declaration applying to some types
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void declaration of a typeless variable
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volatile prefix declaration meaning the variable can be changed at any time
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while executable statement, while loop or do-while loop
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Basic types
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Type Description
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char character type, usually one byte ( a string is array of char )
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int integer type, usually 2 or 4 bytes ( default )
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float floating point type, usually 4 bytes
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double floating point type, usually 8 bytes
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void no type, typeless
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enum enumeration type ( user defines the type name )
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Type modifiers, prefix for basic types
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Modifiers Description
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signed has a sign ( default )
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unsigned no sign bit in variable
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long longer version of type (short or long alone means short int or
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short shorter version of type long int because int is the default)
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const variable can not be stored into
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Storage Types
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Prefix Description
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auto local variable ( default )
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static permanent when function exits, not auto
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volatile can change from outside influence
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extern variables are defined elsewhere, externally
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register assign variable to register
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Operators
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( ) grouping parenthesis, function call
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[ ] array indexing, also [ ][ ] etc.
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-> selector, structure pointer
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. select structure element
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! relational not, complement, ! a yields true or false
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~ bitwise not, ones complement, ~ a
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++ increment, pre or post to a variable
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-- decrement, pre or post to a variable
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- unary minus, - a
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+ unary plus, + a
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* indirect, the value of a pointer, * p is value at pointer p address
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& the memory address, & b is the memory address of variable b
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sizeof size in bytes, sizeof a or sizeof (int)
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(type) a cast, explicit type conversion, (float) i, (*fun)(a,b), (int*)x
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* multiply, a * b
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/ divide, a / b
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% modulo, a % b
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+ add, a + b
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- subtract, a - b
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<< shift left, left operand is shifted left by right operand bits
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>> shift right, left operand is shifted right by right operand bits
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< less than, result is true or false, a %lt; b
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<= less than or equal, result is true or false, a <= b
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> greater than, result is true or false, a > b
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>= greater than or equal, result is true or false, a >= b
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== equal, result is true or false, a == b
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!= not equal, result is true or false, a != b
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& bitwise and, a & b
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^ bitwise exclusive or, a ^ b
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| bitwise or, a | b
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&& relational and, result is true or false, a < b && c >= d
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|| relational or, result is true or false, a < b || c >= d
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? exp1 ? exp2 : exp3 result is exp2 if exp1 != 0, else result is exp3
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= store
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+= add and store
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-= subtract and store
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*= multiply and store
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/= divide and store
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%= modulo and store
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<<= shift left and store
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>>= shift right and store
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&= bitwise and and store
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^= bitwise exclusive or and store
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|= bitwise or and store
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, separator as in ( y=x,z=++x )
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Operator precedence
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More precedence
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LR ( ) [ ] -> . x++ x--
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RL ! ~ - + ++x --x * & sizeof (type)
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LR * / %
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LR + -
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LR << >>
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LR < <= > >=
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LR == !=
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LR &
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LR ^
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LR |
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LR &&
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LR ||
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RL ? :
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RL = += -= *= /= %= >>= <<= &= ^= |=
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LR ,
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Less precedence
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Conditional branching
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if ( condition ) statement ;
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else statement_2 ; /* optional else clause */
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Switch statement
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switch ( expression ) /* constants must be unique */
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{
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case constant_1: /* do nothing for this case */
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break;
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case constant_2: /* drop through and do same as constant_3*/
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case constant_3:
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statement_sequence /* can have but does not need { } */
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break;
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case constant_4:
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statement_sequence /* does this and next */
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/* statement_sequence also*/
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case constant_5:
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statement_sequence
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break;
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default: /* default executes if no constant equals*/
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statement_sequence /* the expression. This is optional */
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}
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Function definition
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type function_name(int a, float b, const char * ch,...) { function_body }
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/* only parameters passed by address can are modified*/
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/* in the calling function, local copy can be modified*/
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char * strcpy( char * s1, const char * s2 ) { statements }
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Declarations forms
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basic_type variable;
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type variable[val][val]...[val]={data,data,...}; /*multidimensional array*/
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struct struct_name { /* struct_name is optional */
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type variable_1; /* any declaration */
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… /* all variable names must be unique*/
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} variable_1, ... ; /* variables are optional */
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struct struct_name { /* struct_name is optional */
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type variable_1: length; /* any declaration : length in bits */
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... /* type is int, unsigned or signed */
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} variable_1, ... ; /* variables are optional, they can also be arrays and pointers */
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union union_name { /* union_name is optional */
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type variable_1; /* variable_1 overlays variable_2 */
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type variable_2;
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...
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} variable_a, ...; /* variables are optional */
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enum enum_type /* enum_name is optional */
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{ enumeration_name_1, /* establishes enumeration literals */
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enumeration_name_2=number,/* optional number, */
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... /* default is 0, 1, 2, ... */
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} variable, ...; /* variables are optional */
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/* use dot notation to select a component of a struct or union */
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