c language summarycmichael/c_lecture/part1.pdfhere, just keep the basics in mind. csc 4103 operating...

CSC 4103 Operating SystemsFall 2008 – Lecture 2 – C Summary

C Language Summary

Chris J Michael

[email protected]

28 August 2008

Heavily Influenced by the GNU C Reference Manual: http://www.gnu.org/software/gnu-c-manual/

http://www.csc.lsu.edu/


Introduction

2

-C98, or the original ANSI C standard

-Lower level than C++ & Java

-gcc: The GNU C compiler



Hello World

3

$ gcc hello.c -o hello.out

$ ./hello.out

Hello World

$ _

#include <stdio.h>

int main(void)

{

printf("Hello World\n");

return 0;

}



Hello World

4

#include <stdio.h>

int main(void)

{


return 0;

}

Whitespace is ignored

#include <stdio.h>

int main(void){printf("Hello World\n");return 0;}



Hello World

5

#include <stdio.h>

int main(void)

{


return 0;

}

Include the library that

provides printing functions



Hello World

6

#include <stdio.h>

int main(void)

{


return 0;

}

Every C program must have

a main function

int main(void)

The main function returns an integer value.

It must be named “main”.

In this case, it does not receive any parameters.



Hello World

7

#include <stdio.h>

int main(void)

{


return 0;

}

The scope encloses the

function body



Hello World

8

#include <stdio.h>

int main(void)

{


return 0;

}

Call the print function with

the desired argument


Call the function “printf”

Send it the string to print

End statements with a semicolon



Hello World

9

#include <stdio.h>

int main(void)

{


return 0;

}

Call the print function with

the desired argument


Strings literalsare enclosed

in double-quotes.

“\n” represents a new line



Hello World

10

#include <stdio.h>

int main(void)

{


return 0;

}

Since main is defined to

return an integer – usually a

zero is returned



Identifiers

11

-Used to name variables, functions, and user-

defined data types

-A group of letters, decimal digits, “_”

-Cannot start with a number

-Examples:foo my_var a1 Something_Clever_1 x

C is case-sensitive!



Constants

12

-Integer Constants:

-Character Constants:

-Real Number Constants:

-String Constants:

138 23 4002145 032 0x1f1f

Octal

Hexidecimal

'c' 'X' '\n' '\'' '\\' '\"'

Enclosed in

single-quotes

„ \ “

3.14 5. .1 0.2 500e9 3e-5

Exponent

"It’s a trap."

"It’s a" " trap."

"It’s\

a trap."

"It’s\na\ntrap."

"\"It’s a trap\""

Equivalent

It‟s

a

trap.

“It‟s a trap.”



Constants

13

-Integer Constants:

-Character Constants:

-Real Number Constants:

-String Constants:

138 23 4002145 032 0x1f1f

Octal

Hexidecimal

'c' 'X' '\n' '\'' '\\' '\"'

Enclosed in

single-quotes

„ \ “

3.14 5. .1 0.2 500e9 3e-5

Exponent

"It’s a trap."

"It’s a" " trap."

"It’s\

a trap."

"It’s\na\ntrap."

"\"It’s a trap\""

Equivalent

It‟s

a

trap.

“It‟s a trap.”



Primitive Data Types

14

-Integer types

-Real number types

unsigned char /* Holds a value from 0 to 256 */

signed char /* Holds a value from -127 to 128 */

char /* May either be unsigned char or signed car depending on

the system. This type should be used for character

constants. */

int /* Holds a value from -2,147,483,648 to 2,147,483,647 */

unsigned int /* Holds a value from 00000000000000 to 4,294,967,647 */

Sizes may change from

system to system!

float /* Single precision floating point */

double /* Double */Enclose comments in these



Enumeration Definitions

15

-Used to name integer valuesenum operating_system

{

BSD, /* The value of BSD will be 0 */

LINUX, /* LINUX will be 1, etc. */

MS_WIN,

DOS,

TOS

};

enum

{

SLACKWARE=23, /* Here we set the first item to 23... */

FEDORA, /* so FEDORA will be 24, etc. */

GENTOO,

DEBIAN

};

Naming is optional



Structure Definitions

16

-A programmer defined type made of

variables and other data types.struct particle

{

int x, y, z;

float velocity_x;

float velocity_y;

float velocity_z;

};

Members are declared like

variables are normally declared

You should provide a name



Structure Declarations

17

-At definition

-After definition

struct particle

{

int x, y, z;

float velocity_x;

float velocity_y;

float velocity_z;

} particle_a, particle_b;

struct particle

{

int x, y, z;

float velocity_x;

float velocity_y;

float velocity_z;

};

...

struct particle particle_a, particle_b;

This way is usually preferred



Structure Member Access

18

-Use the member access operator, the '.'struct particle

{

int x, y, z;

float velocity_x;

float velocity_y;

float velocity_z;

};

...

struct particle particle_a, particle_b;

particle_a.x = 4; particle_a.y = -4; particle_a.z = 1;

particle_a.velocity_x = 1.0;

particle_a.velocity_y = 12e3;

particle_a.velocity_z = 0;



Structure Member Access

19

-Of course, structures may contain other structuresstruct point

{

int x, y, z;

};

struct velocity

{

float x, y, z;

};

struct particle

{

struct point p;

struct velocity v;

};

...

struct particle particle_a;

particle_a.p.x = 4; particle_a.v.x = 1.0;



Array Declarations and Access

20

-Specify type and amount when declaring

-Specify array element when accessing

int my_int_array[10];

struct particle particles[10][10];

my_int_array[0] = 9; /* The first element */

my_int_array[9] = 46; /* The last element */

particles[3][7].p.x = 4;

This structure was defined in the last slide

Careful not to overstep array boundaries! The

compiler may not warn you about this!

my_int_array[10] = 6;

my_int_array[-1] = 0;

Multidimensional, 10x10 array



Strings

21

-Strings are just arrays of characters

char my_string[20] = "Hello World";

my_string = "Hello World";

H e l l o W o r l d \0

my_string[5] = '\0';

H e l l o \0 W o r l d \0

The null character

Hello World

Hello

You cannot assign string literals after initialization!

Initialization

But don't worry! There are some library

functions that help us copy string literals

into arrays. More on that later.



Strings

22







The null character

Hello World

Hello


Initialization






Strings

23







The null character

Hello World

Hello


Initialization






Pointers

24

There is nothing difficult

here, just keep the basics

in mind.



Pointers

25

-Pointers hold memory addresses of stored variables

-You can create a pointer for any data type.

-The two basic operators:

Indirection Address



Pointers

26

-Keep the memory model in mind

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

These are addresses of the

memory locations

These are the contents of

the memory locations

The denotes uninitialized

or junk data in memory



Pointer Declarations

27

-To declare a pointer of any type, simply use the

indirection operator before the

identifier

-Use caution when declaring

multiple pointers at once

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

int *p_to_int;

float *p_to_f1, *p_to_f2;

int *p1, *p2, i1;

These are pointers

This is an integer



Pointer Access

28

-Use the address operator to set a pointer

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

int i = 0; /* Will be located at 0x05 */

int j = 1; /* Will be located at 0x07 */

int *p = &i; /* Will be located at 0x09 */



Pointer Access

29


0x00

0x01

0x02

0x03

0x04

0x05 0

0x06

0x07

0x08

0x09






Pointer Access

30


0x00

0x01

0x02

0x03

0x04

0x05 0

0x06

0x07 1

0x08

0x09






Pointer Access

31


0x00

0x01

0x02

0x03

0x04

0x05 0

0x06

0x07 1

0x08

0x09 0x05






Pointer Access

32


0x00

0x01

0x02

0x03

0x04

0x05 0

0x06

0x07 1

0x08

0x09 0x05




Don't let this

initialization confuse

you. All we're really

doing is

int *p;

...

p = &i;



Pointer Access

33


0x00

0x01

0x02

0x03

0x04

0x05 0

0x06

0x07 1

0x08

0x09 0x05




*p = 4;

p = &j;

*p = 7;

i = *p;



Pointer Access

34


0x00

0x01

0x02

0x03

0x04

0x05 4

0x06

0x07 1

0x08

0x09 0x05




*p = 4;

p = &j;

*p = 7;

i = *p;



Pointer Access

35


0x00

0x01

0x02

0x03

0x04

0x05 4

0x06

0x07 1

0x08

0x09 0x07




*p = 4;

p = &j;

*p = 7;

i = *p;



Pointer Access

36


0x00

0x01

0x02

0x03

0x04

0x05 4

0x06

0x07 7

0x08

0x09 0x07




*p = 4;

p = &j;

*p = 7;

i = *p;



Pointer Access

37


0x00

0x01

0x02

0x03

0x04

0x05 7

0x06

0x07 7

0x08

0x09 0x07




*p = 4;

p = &j;

*p = 7;

i = *p;

This is called a

dereference, it obtains

the value stored at the

memory location the

pointer holds



Pointers to Structures

38

-Similar concept

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

struct loc

{

int x, y, z;

};

struct loc l; /* Will start at 0x02 */

struct loc *p; /* Will be at 0x08 */

l.x = 0; l.y = 1; l.z = 0;

p = &l




39

-Similar concept

0x00

0x01

0x02 0

0x03 1

0x04 0

0x05

0x06

0x07

0x08

0x09

struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l


40

-Similar concept

0x00

0x01

0x02 0

0x03 1

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l

p->x = 2;

p->y = 4;


41

-Similar concept

0x00

0x01

0x02 0

0x03 1

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09

Indirect member

access operator



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l

p->x = 2;

p->y = 4;


42

-Similar concept

0x00

0x01

0x02 2

0x03 1

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l

p->x = 2;

p->y = 4;


43

-Similar concept

0x00

0x01

0x02 2

0x03 4

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09

p->y is the same as (*p).y



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l

p->x = 2;

p->y = 4;

l.x = p->z;


44

-Similar concept

0x00

0x01

0x02 2

0x03 4

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09



struct loc

{

int x, y, z;

};



l.x = 0; l.y = 1; l.z = 0;

p = &l

p->x = 2;

p->y = 4;

l.x = p->z;


45

-Similar concept

0x00

0x01

0x02 0

0x03 4

0x04 0

0x05

0x06

0x07

0x08 0x02

0x09



-Common Type Specifier: const

-Common Storage Specifier: extern

const float pi = 3.14159;

Type and Storage Specifiers

46

extern int seconds;

...

int seconds = 3600;

pi is declared as

read only

seconds is visible

to all files linked the

your project

Must have an "extern" and

"non-extern" declaration



-An expression is one operand and zero or more operators

13

36 + 16

calculate_sum(1, 1)

(8 * (12 + 4))

Expressions

47

addition operator

constants may be operands

functions with return values may be operands

use parentheses to group

expressions -- innermost expressions

are evaluated first



Unary Operators

48

Increment: ++x x++

Decrement: --x x--

Positive: +x

Negative: -x

Logical Negation: !x

Bitwise Negation: ~x

Address: &x

Indirection: *x

Size of: sizeof(x)

Type casting: (int)x (float)x (type)x

Array Subscript: x[3]



Binary Operators

49

Addition: x + y

Subtraction: x - y

Multiplication: x * y

Division: x / y

Modulus: x % y

Bit shift: x << y

Bitwise AND: x & y

Bitwise OR: x | y

Bitwise XOR: x ^ y

Comparison: x == y x != y x < y

x <= y x > y x >= y

Logical: x && y x || y

Assignment: x = y

Compound Assignment: x += y x -= y x *= y

x /= y etc.

Be careful about types



Binary Operators

50

Comma: x, y

Member Access: x.y x->y

The Ternary Operator

x ? y : z



Next Time

51

-A closer look at the highlighted operators

-Statements: actions and control flow

-Functions

-Program structure

-Helpful code snippets


CSC 4103 Operating SystemsFall 2008 – Lecture 2 – C Summary 52


c language summarycmichael/c_lecture/part1.pdfhere, just keep the basics in mind. csc 4103 operating...

Documents