programacion en c para pic mplaide

8/10/2019 programacion en c para pic mplaide

1/443

2010 Microchip Technology Incorporated. All Rights Reserved. Slide 11421 CPL

Introduction to theC Programming Language

Au th or: Rob Os tap iu k

Microchip Technology Inc.


2/443

AgendaDay One - Morning

Using C in an embedded environment

CommentsVariables, identifiers and data types

Literal constants


Symbolic constants

printf() Library Function

Operators


3/443

AgendaDay One Afternoon

Expressions and statements

Making decisionsLoops

Functions


Multi-File projects & storage class

specifiers


4/443

AgendaDay Two

Arrays

Data pointersFunction pointers

Structures


Unions

Bit fields

EnumerationsMacros with #define


5/443


Using C in an Embedded

Environment


6/443

Just the Facts

C was developed in 1972 in order to write

the UNIX operating system

C is more "low level" than other high level

languages (good for MCU programming)


C is supported by compilers for a widevariety of MCU architectures

C can do almostanything assembly

language can do

C is usually easier and faster for writing

code than assembly language


7/443

Busting the MythsThe truth shall set you free

C is not as portable between architectures

or compilers as everyone claims

ANSI language features ARE portable

Processor specific libraries are NOT portable


Processor specific code (peripherals, I/O,interrupts, special features) are NOT portable

C is NOT as efficient as assembly

A goodassembly programmer can usual lydobetter than the compiler, no matter what the

optimization level C WILL use more memory


8/443

Busting the MythsThe truth shall set you free

There is NO SUCH THING as self

documenting code despite what many C

proponents will tell you

C makes it possible to write very confusing


code contests (www.ioccc.org)

Not every line needs to be commented, but

most b locksof code should be

Because of many shortcuts available, C is

not always friendly to new users hence

the need for comments!


9/443

Development Tools Data Flow

C CompilerC Source Files

Assembly Source Files

Assembly Source Files

Compiler

DriverProgram

Assembler

(.asm or .s)


.a Linker

Archiver(Librarian)

MPLAB IDEDebug Tool

Object

Files

Object File Libraries

(Archives)

Linker ScriptCOFF

Debug File

Executable

Memory Map

(.asm or .s)

(.lib or .a)

(.lkr or .gld)


10/443

Development Tools Data Flow

C Compiler

C Source File C Header FilePreprocessor .h.c


Compiler

.sAssembly Source File


11/443

C Runtime Environment

C Compiler sets up a runtime environment

Allocates space for stack

Initializes stack pointer

Allocates space for heap


Copies values from Flash/ROM to variables inRAM that were declared with initial values

Clear uninitialized RAM

Disable all interruptsCall main() function (where your code starts)


12/443

C Runtime Environment

Runtime environment setup code is

automatically linked into application by

most PICMCU compiler suites

Usual lycomes from either:


C30: crt0.s / crt0.o (crt = C RunTime)C18: c018.c / c018.o

User modifiable if absolutely necessary

Details will be covered in compiler specific

classes


13/443

Example

Fundamentals of CA Simple C Program

#include

#define PI 3.14159

Header File

Constant Declaration

(Text Substitution Macro)

Preprocessor

Directives


int main(void){

float radius, area;

//Calculate area of circleradius = 12.0;area = PI * radius * radius;printf("Area = %f", area);

}

Function

Variable Declarations

Comment


14/443


Comments


15/443

Definition

Comments

CommentsComments areare usedused toto documentdocument aa program'sprogram's functionalityfunctionality

andand toto explainexplain whatwhat aa particularparticular blockblock oror lineline ofof codecode doesdoes..CommentsComments areare ignoredignored byby thethe compiler,compiler, soso youyou cancan typetypeanythinganything youyou wantwant intointo themthem..


Two kinds of comments may be used:Block Comment

/* This is a comment */Single Line Comment

// This is also a comment


16/443

CommentsUsing Block Comments

Block comments:

Begin with /*/* and end with */*/

May span multiple lines

****************************************************************************************************************


* Program: hello.c* Program: hello.c* Author: R. Ostapiuk* Author: R. Ostapiuk********************************************************/********************************************************/#i nc l ude#i nc l ude

/* Function: main() *//* Function: main() */intintmainmain((voidvoid)){{printfprintf((Hello, world!Hello, world!\\nn);); /* Display Hello, world! *//* Display Hello, world! */}}


17/443

CommentsUsing Single Line Comments

Single line comments:

Begin with //// and run to the end of the line

May notspan multiple lines

==============================================================================================================


// Program: hello.c// Program: hello.c// Author: R. Ostapiuk// Author: R. Ostapiuk//=======================================================//=======================================================#i nc l ude#i nc l ude

// Function: main()// Function: main()intintmainmain((voidvoid)){{printfprintf((Hello, world!Hello, world!\\nn);); // Display Hello, world!// Display Hello, world!}}


18/443

CommentsNesting Comments

Block comments may not be nested within

other delimited comments

Single line comments may be nested


/*/*c ode her ec ode her e // Comment within a comment// Comment within a comment

*/*/

/*/*c ode her ec ode her e /* Comment within a comment *//* Comment within a comment */c ode her ec ode her e /* Comment within a oops! *//* Comment within a oops! */

*/*/

Example: Delimited comment within a delimited comment.Example: Delimited comment within a delimited comment.

Delimiters dont match up as intended!Delimiters dont match up as intended!

Dangling delimiter causes compile errorDangling delimiter causes compile error


19/443

CommentsBest Practices

/********************************************************/********************************************************* Program: hello.c* Program: hello.c* Author: R. Ostapiuk* Author: R. Ostapiuk

********************************************************/********************************************************/#i nc l ude#i nc l ude

/********************************************************/********************************************************


unc on: ma nunc on: ma n

********************************************************/********************************************************/intintmainmain((voidvoid)){{/*/*int i;int i; // Loop count variable// Loop count variable

char *p; // Pointer to text stringchar *p; // Pointer to text string*/*/

printfprintf((Hello, world!Hello, world!\\nn);); // Display Hello, world!// Display Hello, world!}}


20/443


Variables, Identifiers

and Data Types


21/443

Example

Variables and Data Types

A Simple C Program

#include

#define PI 3.14159

int main(void)


Variable Declarations

Types

Variablesin use

{float radius, area;

//Calculate area of circleradius = 12.0;

area = PI * radius * radius;printf("Area = %f", area);

}


22/443

Variables

A variable may be thought of as a container that

Definition

AA variablevariable isis aa namename thatthat representsrepresents oneone or or moremore

memorymemory locationslocations usedused toto holdhold programprogram datadata..


intmyVariable;

myVariable = 5;

55


23/443

Variables

015 Data Memory (RAM)

Variables are names for

storage locations in

memory


4116

5.74532370373175

10-44

n warp_ ac or;

float length;

char first_letter; A


24/443

Variables


Variable declarations

consist of a unique

identifier (name)


float length;

char first_letter;

n warp_ ac or; 4116

5.74532370373175

10-44

A


25/443

Variables


and a data type

Determines size

Determines how valuesare interpreted


float length;

char first_letter;

n warp_ ac or; 4116

5.74532370373175

10-44

A


26/443

Example of Identifiers in a Program

Identifiers

Names given to program elements:

Variables, Functions, Arrays, OtherElements


.

#define PI 3.14159

int main(void){

float radius, area;

//Calculate area of circleradius = 12.0;area = PI * radius * radius;printf("Area = %f", area);

}


27/443

Identifiers

Valid characters in identifiers:

I d e n t i f i e rFirst Character Remainin Characters


Case sensitive!Only first 31 characters significant*

_ (underscore)A to Z

a to z

_ (underscore)A to Z

a to z

0 to 9


28/443

ANSI C Keywords

autobreak

casechar

doubleelse

enumextern

intlong

registerreturn

structswitch

typedefunion


continuedefault

do

forgoto

if

signedsizeof

static

voidvolatile

whileSome compiler implementations may define

additional keywords


29/443

Data Types

Fundamental Types

Type Description Bits

charchar

intintfloatfloatdoubledouble

single charactersingle character

integerinteger

single precision floating point numbersingle precision floating point number

double precision floating point numberdouble precision floating point number

1616

88

3232

6464


The size of an int varies from compiler to compiler MPLAB C30 int is 16 bits

MPLAB C18 int is 16 bits CCS PCB, PCM & PCH int is 8 bits HI-TECH PICC Compiler int is 16 bits


30/443

Data Type Qualifiers

Modified Integer Types

Qualifiers: unsigned, signed, short and long

Qualified Type Min Max Bits

unsignedcharchar, signedchar

unsigned shorti nt

0

-128

0

255

127

65535

8

8

16


shorti nt, signed short ntunsignedi nt

int, signedi ntunsigned longi nt

longi nt, signed longi ntunsigned long longi nt

long longi nt,signed long longi nt

-32768

0

-32768

0

-231

0

-263

32767

65535

32767

231-1

263-1

232-1

264-1

16

16

16

32

64

32

64


31/443

Data Type Qualifiers

Modified Floating Point Types

Qualified Type Absolute Min Bits

floatfloat

doubledouble

long doublelong double

~10~10--44.8544.85

~10~10--44.8544.85

~10~10--323.3323.3

3232

3232

6464

Absolute Max

~10~1038.5338.53

~10~1038.5338.53

~10~10308.3308.3

(1)(1)


MPLAB C30: (1)double is equivalent to longdouble if fno-short-double is used

MPLAB C30 Uses the IEEE-754 Floating Point Format

MPLAB C18 Uses a modified IEEE-754 Format


32/443

Variables

How to Declare a Variable

A variable must be declared before it can beused

Syntax

t y pet y pei dent i f i eri dent i f i er11, i dent i f i er, i dent i f i er22, , i dent i f i e r, , i dent i f i e rnn;;


allocate and how the values should be handled

Example

intint xx,, yy,, zz;;floatfloatwarpFactorwarpFactor;;charchar text_buffer[10]text_buffer[10];;unsignedunsignedindexindex;;


33/443

Syntax

Variables


Variables may be declared in a few ways:

t y pet y pei dent i f i eri dent i f i er;;

One declaration on a lineOne declaration on a line


t y pet y pei dent i f i eri dent i f i er ==I n i t i a l Val ueI n i t i al Va l ue;;

t y pet y pei den t i f i eri den t i f i er11,, i dent i f i eri dent i f i er22,, i dent i f i eri dent i f i er33;;

t y pet y pei den t i f i eri den t i f i er11 ==Va l ueVa l ue11,, i dent i f i eri dent i f i er22 ==Va l ueVa l ue22;;

One declaration on a line with an initial valueOne declaration on a line with an initial value

Multiple declarations of the same type on a lineMultiple declarations of the same type on a line

Multiple declarations of the same type on a line with initial valuesMultiple declarations of the same type on a line with initial values


34/443

Examples

Variables


unsigned intunsigned int xx;;

unsignedunsignedyy == 1212;;intint aa,,bb,, cc;;lon intlon intm Varm Var == 0x123456780x12345678;;


longlong zz;;charchar firstfirst == 'a''a',, secondsecond,, thirdthird == 'c''c';;floatfloatbig_numberbig_number == 6.02e+236.02e+23;;

It is customary for variable names to be spelled using "camel case", where the initial letter

is lower case. If the name is made up of multiple words, all words after the first will start

with an upper case letter (e.g. myLongVarName).


35/443

Variables


Sometimes variables (and other program

elements) are declared in a separate file

called a header file

Header file names customarily end in .h


Header files are associated

with a program through the

#include directive

MyProgram.h

MyProgram.c


36/443

#include Directive

Three ways to use the #include directive:

Syntax

#include#includeLook for file in the compiler search pathLook for file in the compiler search path

The com iler search ath usuall includes the com iler's directorThe com iler search ath usuall includes the com iler's director


and all of its subdirectories.and all of its subdirectories.

For example: C:For example: C:\\Program FilesProgram Files\\MicrochipMicrochip\\MPLAB C30MPLAB C30\\*.**.*

#include#include file.hfile.h

Look for file in project directory onlyLook for file in project directory only

#include#include c:c:\\MyProjectMyProject\\file.hfile.hUse specific path to find include fileUse specific path to find include file


37/443

main.h main.c

#include Directivemain.h Header File and main.c Source File

unsigned intunsigned int a;a;unsigned intunsigned intb;b;unsigned intunsigned int c;c;

#include#include "main.h""main.h"

intintmain(main(voidvoid))


a =a = 55;;b =b = 22;;c = a+b;c = a+b;

}}

The contents of main.hThe contents of main.h

areare effectivelyeffectivelypasted intopasted into

main.c starting at themain.c starting at the#include#include directives linedirectives line


38/443

main.c

#include DirectiveEquivalent main.c File

unsigned intunsigned int a;a;unsigned intunsigned intb;b;unsigned intunsigned int c;c;

After the preprocessor

runs, this is how the

compiler sees themain.c file

The contents of the


Equivalent main.c fileEquivalent main.c filewithoutwithout #include#include

intintmain(main(voidvoid)){{

a =a = 55;;b =b = 22;;

c = a+b;c = a+b;}}

header file arentactual lycopied to your

main source file, but it

will behave as iftheywere copied


39/443


Lab Exercise 1

Variables and Data Types


40/443

Lab 01Variables and Data Types

Open the projects workspace:

On the lab PCOn the lab PC

C:C:\\MastersMasters\\14211421\\Lab01Lab01\\Lab01.mcwLab01.mcw


1Open MPLABOpen MPLAB IDE and selectIDE and select OpenOpen

WorkspaceWorkspace from thefrom the FileFile menu.menu.Open the file listed above.Open the file listed above.

If you already have a project openIf you already have a project open

in MPLAB IDE, close it byin MPLAB IDE, close it byselectingselecting Close WorkspaceClose Workspace fromfrom

thethe FileFile menu before opening amenu before opening anew one.new one.

L b 01


41/443


Compile and run the code:

Compile (Build All)Compile (Build All) RunRun2 3 HaltHalt4


2 Click on theClick on the Build AllBuild All button.button.

3 If no errors are reported,If no errors are reported,

click on theclick on the RunRun button.button.

4 Click on theClick on the HaltHalt button.button.

L b 01


42/443


Expected Results (1):


5 TheThe SIMSIM UartUart11 windowwindow shouldshould showshow thethe texttext thatthat

isis outputoutput byby thethe program,program, indicatingindicating thethe sizessizes ofofCsCs datadata typestypes inin bytesbytes..

L b 01


43/443




6 TheThe watchwatch windowwindow shouldshould showshow thethe valuesvalues whichwhich

areare storedstored inin thethe variablesvariables andand makemake itit easiereasier totovisualizevisualize howhow muchmuch spacespace eacheach oneone requiresrequires inin

datadata memorymemory (RAM)(RAM)..

L b 01


44/443

0x08A80x08A80x08A90x08A9


0000

323232

0x08AA0x08AA

0x08AC0x08AC

0x08AE0x08AE

0x08AB0x08AB

0x08AD0x08AD

0x08AF0x08AF

charcharshort intshort intintint

Variables in MemoryVariables in Memory71616--bit Data Memorybit Data Memory


00004200

4200

32004800

4800

0x08B00x08B00x08B20x08B2

0x08B40x08B4

0x08B60x08B6

0x08B80x08B8

0x08BA0x08BA

0x08BC0x08BC

0x08B10x08B10x08B30x08B3

0x08B50x08B5

0x08B70x08B7

0x08B90x08B9

0x08BB0x08BB

0x08BD0x08BD

long intlong int

floatfloat

doubledouble

MultiMulti--byte valuesbyte values

stored in "Littlestored in "Little

Endian" formatEndian" format

on PICon PICmicrocontrollersmicrocontrollers

Lab 01


45/443


What does the code do?

START

Declare Constant #define CONSTANT1 50

Example lines of code from the demo program:


Initialize Variables

Print Variable

Sizes

Loop

Forever

intVariable = CONSTANT1;

printf("\nAn integer variablerequires %d bytes.",

sizeof(int));

while(1);

Lab 01


46/443

Lab 01Conclusions

Variables must be declared before used

Variables must have a data typeData type determines memory use


Most efficient data types:int on 16-bit architectures

char on 8-bit architectures (if int is 16-bit)

Don't use float/double unless you really

need them


47/443


Literal Constants

A Simple C Program


48/443

Example

unsigned intunsigned int aa;;unsigned intunsigned int cc;;#define#definebb 22

A Simple C ProgramLiteral Constants

Literal


voidvoidmainmain((voidvoid)){{

aa == 55;;

cc == aa ++bb;;printfprintf(("a=%d, b=%d, c=%d"a=%d, b=%d, c=%d\\n"n",, aa,,bb,, cc););}}

Literal

Lit l C t t


49/443

Literal Constants

Definition

AA literalliteral oror aa literalliteral constantconstant isis aa value,value, suchsuch asas aanumber,number, charactercharacter oror string,string, whichwhich maymay bebe assignedassigned toto aa

variablevariable oror aa constantconstant.. ItIt maymay alsoalso bebe usedused directlydirectly asas aafunctionfunction parameterparameter oror anan operandoperand inin anan expressionexpression..


era s

Are "hard coded" values

May be numbers, characters or strings

May be represented in a number of formats(decimal, hexadecimal, binary, character, etc.)

Always represent the same value (5 alwaysrepresents the quantity five)

Constant vs Literal


50/443

Constant vs. LiteralWhat's the difference?

Terms are used interchangeably in most

programming literature

A literal is a constant, but a constant is nota literal


#defineMAXINT 32767const intMAXINT = 32767;

For purposes of this presentation:

Constants are labels that represent a literal

Literals are values, often assigned to symbolic

constants and variables

Lit l C t t


51/443

Literal Constants

Four basic types of literals:

Integer

Floating Point

Character


String

Integer and Floating Point are numer ic

typeconstants:

Commas and spaces are not allowedValue cannot exceed type bounds

May be preceded by a minus sign

Integer Literals


52/443

Integer LiteralsDecimal (Base 10)

Cannot start with 0 (except for 0 itself)

Cannot include a decimal point

Valid Decimal Integers:


Invalid Decimal Integers:-

32,767 25.0 1 024 0552

Integer Literals


53/443

Integer LiteralsHexadecimal (Base 16)

Must begin with 0x or 0X (thats zero-x)

May include digits 0-9 and A-F / a-f

Valid Hexadecimal Integers:


Invalid Hexadecimal Integers:x x x x

0x5.3 0EA12 0xEG 53h

Integer Literals


54/443

Integer LiteralsOctal (Base 8)

Must begin with 0 (zero)

May include digits 0-7Valid Octal Integers:


Invalid Octal Integers:

05.3 0o12 080 53o

While Octal is still part of the ANSI specification, almost noWhile Octal is still part of the ANSI specification, almost no

one uses it anymore.one uses it anymore.

Integer Literals


55/443

Integer LiteralsBinary (Base 2)

Must begin with 0b or 0B (thats zero-b)

May include digits 0 and 1

Valid Binary Integers:


Invalid Binary Integers:

0b1.0 01100 0b12 10bANSI C doesANSI C does notnotspecify a format for binary integer literals.specify a format for binary integer literals.

However, this notation is supported by most compilers.However, this notation is supported by most compilers.

Integer Literals


56/443

Integer LiteralsQualifiers

Like variables, literals may be qualified

A suffix is used to specify the modifier

U or u for unsigned: 25u

L or l for lon : 25L


'F' or 'f' for float: 10f or 10.25FSuffixes may be combined: 0xF5UL

Note: U must precede L

Numbers without a suffix are assumed to

be signed and short

Floating Point Literals


57/443

gDecimal (Base 10)

Like decimal integer literals, but

decimal point is allowed

e notation is used to specify

n


Valid Floating Point Literals:

Invalid Floating Point Literals:

2.56e-5 10.4378 48e8 0.5 10f

0x5Ae-2 02.41 F2.33

Character Literals


58/443

Character Literals

Specified within single quotes (')

May include any single printable characterMay include any single non-printable


c arac er us ng escape sequences e.g.

'\0' = NUL) (also called digraphs)

Valid Characters: 'a', 'T', '\n', '5',

'@', ' ' (space)

Invalid Characters: 'me', '23', '''

String Literals


59/443

String Literals

Specified within double quotes (")

May include any printable or non-printable

characters (using escape sequences)

Usually terminated by a null character \0


Valid Strings: "Microchip", "Hi\n","PIC", "2500","[email protected]","He said, \"Hi\""

Invalid Strings: "He said, "Hi""

String Literals


60/443

gDeclarations

Strings are a special case of arrays

If declared without a dimension, the null

character is automatically appended to theend of the string:


charchar colorcolor[[33] =] = "RED""RED";;

Is stored as:Is stored as:

colorcolor[[00] =] = 'R''R'colorcolor[[11] =] = 'E''E'colorcolor[[22] =] = 'D''D'

NOTNOT a complete stringa complete string no 'no '\\0' at end0' at end

charchar colorcolor[] =[] = "RED""RED";;

Is stored as:Is stored as:

colorcolor[[00] =] = 'R''R'colorcolor[[11] =] = 'E''E'colorcolor[[22] =] = 'D''D'colorcolor[[33] =] = ''\\0'0'

Example 1 Wrong Way Example 2 Right Way

String Literals


61/443

gHow to Include Special Characters in Strings

Escape Sequence Character ASCII Value

\\aa

\\bb\\tt\\nn

BELL (alert)BELL (alert)

BackspaceBackspaceHorizontal TabHorizontal Tab

Newline (Line Feed)Newline (Line Feed)

77

8899

1010


vv

\\ff\\rr\\""\\''\\??\\\\\\00

Vertical TabVertical Tab

Form FeedForm Feed

Carriage ReturnCarriage Return

Quotation Mark (")Quotation Mark (")

Apostrophe/Single Quote (')Apostrophe/Single Quote (')Question Mark (?)Question Mark (?)

Backslash (Backslash (\\))

NullNull

1212

1313

3434

3939

6363

9292

00

String Literals


62/443

Example

How to Include Special Characters in Strings

This string includes a newline character

charcharmessagemessage[] =[] = "Please enter a command"Please enter a command\\n"n"


scape sequences may e nc u e n a

string like any ordinary character

The backslash plus the character that

follows it are considered a singlecharacter and have a single ASCII value


63/443


Symbolic Constants

Symbolic Constants


64/443

Symbolic Constants

Definition

AA constantconstant oror aa symbolicsymbolic constantconstant isis aa labellabel thatthatrepresentsrepresents aa literalliteral.. AnywhereAnywhere thethe labellabel isis encounteredencountered

inin code,code, itit willwill bebe interpretedinterpreted asas thethe valuevalue ofof thethe literalliteral ititrepresentsrepresents..


ons an s

Once assigned, never change their value

Make development changes easy

Eliminate the use of "magic numbers"

Two types of constantsText Substitution Labels

Variable Constants (!!??)

Symbolic ConstantsC t t V i bl U i


65/443

Some texts on C declare constants like:

This is not efficient for an embedded

Constant Variables Using const

Example

constconst floatfloat PIPI == 3.1415933.141593;;


sys em: var a e s a oca e n program

memory, but it cannot be changed due tothe const keyword

This is not the traditional use of constIn the vast majority of cases, it is better touse #define for constants

Symbolic ConstantsT t S b tit ti L b l U i #d fi


66/443

Text Substitution Labels Using #define

Defines a text substitution labelSyntax

#define#definel abel t ex tl abel t ex tEach instance of l abelwill be replaced with t ex tby the


Example

#define#define PIPI 3.141593.14159

#define#definemolmol 6.02E236.02E23#define#defineMCUMCU "PIC24FJ128GA010""PIC24FJ128GA010"#define#define COEF 2 * PICOEF 2 * PI

a e

No memory is used in the microcontroller

Symbolic Constants#d fi Gotchas


67/443

Note: a #define directive is NEVER

terminated with a semi-colon (;), unless

you want that to be part of the textsubstitution.

#define Gotchas


Example

#define#defineMyConstMyConst 55;;

cc ==MyConstMyConst ++ 33;;

cc == 55; +; + 33;;

Symbolic ConstantsInitializing Variables When Declared


68/443

Initializing Variables When Declared

A constant declared with const may not

be used to initialize a global or static

variable when it is declared (though it maybe used to initialize local variables)


Example

#define#define CONSTANT1CONSTANT1 55constconst CONSTANT2CONSTANT2 == 1010;;

intint variable1variable1 == CONSTANT1CONSTANT1;;intint variable2variable2;;// Cannot do: int variable2 = CONSTANT2// Cannot do: int variable2 = CONSTANT2


69/443


Lab Exercise 2

Symbolic Constants

Lab 02Symbolic Constants


70/443

Symbolic Constants





1 Open MPLABOpen MPLAB IDE and selectIDE and select OpenOpen







71/443

Symbolic Constants










72/443

Symbolic Constants




isis outputoutput byby thethe program,program, indicatingindicating thethe valuesvalues ofofthethe twotwo symbolicsymbolic constantsconstants inin thethe codecode..



73/443

Symbolic Constants


CONSTANT1CONSTANT1 hashas

nono addressaddress

CONSTANT2CONSTANT2 has ahas a

program memoryprogram memory


6 TheThe watchwatch windowwindow shouldshould showshow thethe twotwo symbolicsymbolicconstantsconstants declareddeclared inin codecode.. CONSTANTCONSTANT11 waswasdeclareddeclared withwith #define#define,, andand thereforetherefore usesuses nono

memorymemory.. CONSTANTCONSTANT22 waswas declareddeclared withwith constconstandand isis storedstored asas anan immutableimmutable variablevariable inin flashflash

programprogram memorymemory..

address ( )address ( )



74/443

Symbolic Constants



7 IfIf wewe looklook inin thethe programprogram memorymemory window,window, wewe

cancan findfind CONSTANTCONSTANT22 whichwhich waswas createdcreated withwithconstconst atat addressaddress 00xx011011DD00 (as(as waswas shownshown inin thethe

watchwatch window)window)



75/443

y


External Symbols in Program Memory (by name):

0x0011d0 _CONSTANT20x000e16 __Atexit0x000b9c __Closreg


8 IfIf wewe openopen thethe mapmap filefile (in(in thethe lablab0202 projectproject

directory),directory), wewe cancan seesee thatthat memorymemory hashas beenbeenallocatedallocated forforCONSTANTCONSTANT22 atat 00xx011011DD00,, butbut nothingnothinghashas beenbeen allocatedallocated forforCONSTANTCONSTANT11..

0x00057c __DNKfflush0x0012d8 __DefaultInterrupt

CONSTANT1 does not appear anywhere in the map file

a .map


76/443


77/443



printf()Standard Library Function


78/443

Used to write text to the "standard output"

Normally a computer monitor or printer

Often the UART in embedded systems


SIM Uart1 window in MPLAB IDE SIM

printf()Standard Library Function


79/443

Syntax

printfprintf((Cont r o l St r i ngCont r o l St r i ng,, ar g1ar g1,,ar gnar gn););

Everything printed verbatim within string except %d's,which are replaced by the argument values from the list


Example

intint aa == 55,,bb == 1010;;printfprintf(("a ="a = %d%d\\nb =nb = %d%d\\n"n",, aa,,bb););

Result:Result:

a = 5a = 5

b = 10b = 10

NOTE: the 'd' in %d is the

con vers ion character.

(See next slide for details)

printf()Conversion Characters for Control String


80/443

Conversion

Character Meaning

%c%c%s%s%d%d%o%o

Single characterSingle character

String (all characters until 'String (all characters until '\\0')0')Signed decimal integerSigned decimal integer

Unsigned octal integerUnsigned octal integer


uu

%x%x%X%X%f%f%e%e%E%E%g%g%G%G

Unsigned decimal integerUnsigned decimal integer

Unsigned hexadecimal integer with lowercase digits (Unsigned hexadecimal integer with lowercase digits (1a5e1a5e))AsAs xx, but with uppercase digits (e.g., but with uppercase digits (e.g. 1A5E1A5E))

Signed decimal value (floating point)Signed decimal value (floating point)

Signed decimal with exponent (e.g.Signed decimal with exponent (e.g. 1.26e1.26e--55))

AsAs ee, but uses, but uses EE for exponent (e.g.for exponent (e.g. 1.26E1.26E--55))

AsAs ee oror ff, but depends on size and precision of value, but depends on size and precision of value

AsAs gg, but uses, but uses EE for exponentfor exponent

printf()Gotchas


81/443

The value displayed is interpreted entirely

by the formatting string:

printf("ASCII = %d", 'a');will output:ASCII = 97


printf("Value = %d", 6.02e23);will output:Value = 26366

Incorrect results may be displayed if the

format type doesn't match the actual data

type of the argument

printf()Useful Format String Examples for Debugging


82/443

Print a 16-bit hexadecimal value with a

"0x" prefix and leading zeros if necessary

to fill a 4 hex digit value:printf("Address of x =printf("Address of x = %#06x%#06x\\n", x_ptr);n", x_ptr);


# Specifies that a 0x or 0X should precede a hexadecimal value (hasother meanings for different conversion characters)

06 Specifies that 6 characters must be output (including 0x prefix),

zeros will be filled in at left if necessary

x Specifies that the output value should be expressed as a

hexadecimal integer

printf()Useful Format String Examples for Debugging


83/443

Same as previous, but force hex letters to

uppercase while leaving the 'x' in '0x'

lowercase:printf("Address of x = 0xprintf("Address of x = 0x%04X%04X\\n", x_ptr);n", x_ptr);


04 Specifies that 4 characters must be output (no longer including 0xprefix since that is explicitly included in the string), zeros will be

filled in at left if necessary

X Specifies that the output value should be expressed as ahexadecimal integer with uppercase A-F


84/443


Lab Exercise 3


Lab 03printf() Library Function


85/443












86/443










87/443




isis outputoutput byby thethe programprogram bybyprintf()printf(),, showingshowingthethe howhow valuesvalues areare printedprinted basedbased onon thethe

formattingformatting charactercharacter usedused inin thethe controlcontrol stringstring..



88/443


a

25

printfprintf(("'a' as character (c): %c"'a' as character (c): %c\\n"n",, 'a''a'););

printfprintf(("25 as decimal (d): %d"25 as decimal (d): %d\\n"n",, 2525););

Detailed Analysis:Detailed Analysis:Line of Code From Demo ProjectLine of Code From Demo Project OutputOutput


-24058printfprintf(("'Microchip' as decimal (d):"'Microchip' as decimal (d): %d%d\\n"n",, "Microchip""Microchip"););

Microchipprintfprintf(("'Microchip' as string (s): %s"'Microchip' as string (s): %s\\n"n",, "Microchip""Microchip"););

26366printfprintf(("6.02e23 as decimal (d):"6.02e23 as decimal (d): %d%d\\n"n",, 6.02e236.02e23););

6.020000e+23printfprintf(("6.02e23 as exponent (e): %e"6.02e23 as exponent (e): %e\\n"n",, 6.02e236.02e23););

16419

2.550000

97

printfprintf(("2.55 as decimal (d):"2.55 as decimal (d): %d%d\\n"n",, 2.552.55););

printfprintf(("2.55 as float (f): %f"2.55 as float (f): %f\\n"n",, 2.552.55););

printfprintf(("'a' as decimal (d):"'a' as decimal (d): %d%d\\n"n",, 'a''a'););

Lab 03Conclusions


89/443

printf() has limited use in embedded

applications themselves

It is very useful as a debugging tool


can sp ay a a a mos any way you

want

Projects that use printf() must:

Configure a heap (done in MPLAB IDE)

Include the stdio.h header file


90/443


Operators

OperatorsHow to Code Arithmetic Expressions


91/443

Definition

Operands may be variables, constants or

AnAn arithmeticarithmetic expressionexpression isis anan expressionexpression thatthat containscontainsoneone oror moremore operandsoperands andand arithmeticarithmetic operatorsoperators..


A microcontroller register is usually treated asa variable

There are 9 arithmetic operators that may

be usedBinary Operators: +, -, *, /, %

Unary Operators: +, -, ++, --

OperatorsArithmetic


92/443

ModuloModulo%%

AdditionAddition++

MultiplicationMultiplication**

DivisionDivision//

Operator ResultOperation Example

x % yx % y

x + yx + y

x * yx * y

x / yx / yRemainder ofRemainder of xx divided bydivided by yy

Sum ofSum of xx andand yy

Product ofProduct of xx andand yy

Quotient ofQuotient of xx andand yy


NegativeNegative-- (unary)(unary)

SubtractionSubtraction--

PositivePositive++ (unary)(unary)

NOTENOTE -- AnAn intint divided by andivided by an intint returns anreturns an intint::10/3 = 310/3 = 3

Use modulo to get the remainder:Use modulo to get the remainder:

10%3 = 110%3 = 1

--xx

xx -- yy

+x+xNegative value ofNegative value of xx

Difference ofDifference of xx andand yy

Value ofValue of xx

OperatorsDivision Operator


93/443

If both operands are an integer type, the result

will be an integer type (int, char)

If one or both of the operands is a floating pointtype, the result will be a floating point type (float,

double


Example: Integer Divide Example: Floating Point Divide

intint aa == 1010;;intintbb == 44;;floatfloat cc;;

cc == aa //bb;;

intint aa == 1010;;floatfloatbb == 4.0f4.0f;;floatfloat cc;;

cc == a / b;a / b;

c = 2.c = 2.000000000000Because: int / intBecause: int / int intint

c = 2.c = 2.550000000000Because: float / intBecause: float / int floatfloat

OperatorsImplicit Type Conversion


94/443

In many expressions, the type of one

operand will be temporarily "promoted" to

the larger type of the other operandExample


A smaller data type will be promoted to the

largest type in the expression for the

duration of the operation

nn xx == ;;

floatfloat yy == 2.02.0,, zz;;zz == xx ** yy;; // x promoted to float// x promoted to float

OperatorsImplicit Arithmetic Type Conversion Hierarchy


95/443

long long

unsigned long long

float

double

long double

nverte

dto

press

ion


char

int

unsigned intlong

unsigned long

unsigned charSma

llertypes

co

larg

esttypeine

short

unsigned short

OperatorsArithmetic Expression Implicit Type Conversion

E l i li it t i


96/443

Expression Implicit Type Conversion Expression's Type

Assume x is defined as:

short x =short x = --5;5;Result

Example implicit type conversions


--xx xx is promoted tois promoted to intint intint 55

x *x * --2L2L xx is promoted tois promoted to longlongbecausebecause --2L2L is ais a longlong

longlong 1010

8/x8/x xx is promoted tois promoted to intint intint --11

8%x8%x xx is promoted tois promoted to intint intint 33

8.0/x8.0/x xx is promoted tois promoted to doubledoublebecausebecause 8.08.0 is ais a doubledouble

doubledouble --1.61.6


97/443

OperatorsArithmetic: Increment and Decrement



98/443


DecrementDecrement----

IncrementIncrement++++

xx----

----xx

x++x++

++x++x

UseUse xx then decrementthen decrement xx by 1by 1

DecrementDecrement xx by 1, then useby 1, then use xx

UseUse xx then incrementthen increment xx by 1by 1

IncrementIncrement xx by 1, then useby 1, then use xx


xx == 55;;yy == ((x++x++) +) + 55;;

// y = 10// y = 10// x = 6// x = 6

xx == 55;;yy = (= (++x++x) +) + 55;;

// y = 11// y = 11// x = 6// x = 6

Postfix Example Prefix Example

Definition

OperatorsHow to Code Assignment Statements


99/443

Definition

Two types of assignment statements

AnAn assignmentassignment statementstatement isis aa statementstatement thatthat assignsassigns aavaluevalue toto aa variablevariable..


mp e ass gnmen

v ar i ab l e= ex pr es s i on;The expression is evaluated and the result isassigned to the variable

Compound assignmentv ar i ab l e= v ar i ab l e op ex pr es s i on;

The variable appears on both sides of the =

OperatorsAssignment


100/443

--==

*=*=

AssignmentAssignment==

+=+=xx --= y= y

x *= yx *= y

x = yx = y

x += yx += yx = xx = x -- yy

x = x * yx = x * y

AssignAssign xx the value ofthe value of yy

x = x + yx = x + y



>>=>>=

|=|== y

x |= yx |= yx y

x = x | yx = x | yx = x


101/443

Statements with the same variable on each

side of the equals sign:Example

xx == xx ++ yy;;


May use the shortcut assignment

operators (compound assignment):

Example

xx +=+= yy;; //Increment x by the value y//Increment x by the value y

set equal to the current value ofset equal to the current value of xx plus the value ofplus the value of yy

Example

OperatorsCompound Assignment


102/443

p

intint xx == 22;; //Initial value of x is 2//Initial value of x is 2

xx *=*= 55;; //x = x * 5//x = x * 5


e ore s a emen s execu e :e ore s a emen s execu e : xx ==

After statement is executed:After statement is executed: xx = 10= 10x *= 5;x *= 5;x = (x * 5);x = (x * 5);x = (2 * 5);x = (2 * 5);x = 10;x = 10;

Is equivalent to:Is equivalent to:

Evaluate right side first:Evaluate right side first:

Assign result toAssign result to xx::

OperatorsRelational

Operator Result (FALSE = 0 TRUE 0)Operation Example


103/443

Operator Result (FALSE 0, TRUE 0)Operation Example

Greater thanGreater than>>

Less thanLess than= yx >= y

1 if1 if xx equal toequal to yy, else 0, else 0

1 if1 if xx not equal tonot equal to yy, else 0, else 0

1 if1 if xx greater than or equal togreater than or equal to yy,,

else 0else 0

OperatorsDifference Between = and ==

Be careful not to confuseBe careful not to confuse andand


104/443

= is the assignment operator=

Be careful not to confuseBe careful not to confuse == andand ====..

They are not interchangeable!They are not interchangeable!


== is the 'equals to' relational operatorx == 5 tests whether the value of x is 5

ifif ((xx ==== 55))

{{do if value ofdo if value of xx is 5is 5

}}

OperatorsDifference Between = and ==

What happens when the following code is


105/443

Example

What happens when the following code is

executed?

voidvoidmainmain((voidvoid))


{{

intint xx == 22;; //Initialize x//Initialize xifif ((xx == 55)) //If x is 5,//If x is 5,{{

printfprintf(("Hi!""Hi!");); //display "Hi!"//display "Hi!"}}

}}

OperatorsLogical

Operator Result (FALSE = 0 TRUE 0)Operation Example


106/443

Logical ORLogical OR||||

Logical ANDLogical AND&&&&

x || yx || y

x && yx && y

0 if0 if bothboth xx == 00 andand yy == 00,,else 1else 1

1 if1 if bothboth xx 00 andand yy 00,,else 0else 0

Operator Result (FALSE = 0, TRUE 0)Operation Example


Logical NOTLogical NOT!! !x!x 1 if1 if xx == 00, else 0, else 0

In conditional expressions, any non-zero value is

interpreted as TRUE. A value of 0 is always FALSE.

OperatorsBitwise

Operator Result (for each bit position)Operation Example


107/443

p p p

Bitwise ANDBitwise AND&&

Bitwise ORBitwise OR||

x & yx & y

x | yx | y

1, if 1 in both1, if 1 in both xx andand yy0, if 0 in0, if 0 in xx oror yy or bothor both

1, if 1 in1, if 1 in xx oror yy or bothor both0, if 0 in both0, if 0 in both xx andand yy


Bitwise XORBitwise XOR^

Bitwise NOTBitwise NOT(One's Complement)(One's Complement)

~~

x ^ yx ^ y

~x~x

,,

0, if 0 or 1 in both0, if 0 or 1 in both xx andand yy

1, if 0 in1, if 0 in xx0, if 1 in0, if 1 in xx

The operation is carried out on each bit ofthe first operand with each corresponding

bit of the second operand

OperatorsDifference Between & and &&

Be careful not to confuseBe careful not to confuse && andand &&&&


108/443

& is the bitwise AND operator

Be careful not to confuseBe careful not to confuse && andand &&&&..

They are not interchangeable!They are not interchangeable!


&& is the logical AND operator0b1010 && 0b1101 0b0001 (TRUE)&& 1 (TRUE)

ifif ((xx &&&& yy)){{do ifdo if xx andand yyare both TRUE (nonare both TRUE (non--zero)zero)

}}

OperatorsDifference Between & and &&

What happens when each of these code


109/443

What happens when each of these code

fragments are executed?

Example 1 Using A BitwiseAND Operator

charchar xx == 0b10100b1010;;


Example 2 Using A LogicalAND Operator

charchar xx == 0b10100b1010;;charchar yy == 0b01010b0101;;ifif ((xx &&&& yy))printfprintf(("Hi!""Hi!"););

charchar yy == 0b01010b0101;;

ifif ((xx && yy))printfprintf(("Hi!""Hi!"););

OperatorsLogical Operators and Short Circuit Evaluation

The evaluation of expressions in a logical


110/443

p g

operation stops as soon as a TRUE or

FALSE result is knownExample


If we have two expressions being tested in a logical AND operation:If we have two expressions being tested in a logical AND operation:

ex pr 1ex pr 1&&&& ex pr 2ex pr 2The expressions are evaluated from left to right. IfThe expressions are evaluated from left to right. If ex pr 1ex pr 1is 0 (FALSE), thenis 0 (FALSE), then

ex pr 2ex pr 2would not be evaluated at all since the overall result is already knownwould not be evaluated at all since the overall result is already known

to be false.to be false.

ex pr 1 ex pr 2 Result0 X (0) 0

0 X (1) 0

1 0 0

1 1 1

Truth Table for AND (&&)Truth Table for AND (&&)FALSE = 0FALSE = 0

TRUE = 1TRUE = 1

ex pr 2ex pr 2is not evaluatedis not evaluatedin the first two casesin the first two cases

since its value is notsince its value is not

relevant to the result.relevant to the result.

OperatorsLogical Operators and Short Circuit Evaluation

The danger of short circuit evaluation


111/443

Example

g

== ==

IfIf zz = 0, then= 0, then cc willwill notnot be evaluatedbe evaluated


{{

zz +=+= 55;;cc +=+= 1010;;

}}

It is perfectly legal in C to logically compare two assignment expressions inIt is perfectly legal in C to logically compare two assignment expressions in

this way, though it is not usually good programming practice.this way, though it is not usually good programming practice.

A similar problem exists when using function calls in logical operations, whichA similar problem exists when using function calls in logical operations, which

is a very common practice. The second function may never be evaluated.is a very common practice. The second function may never be evaluated.

Initial value ofInitial value of cc may not be correctmay not be correct

OperatorsShift



112/443

Shift LeftShift Left>

x yx >> y

ShiftShift xx byby yy bits to the leftbits to the left

ShiftShift xx byby yy bits to the rightbits to the right


x = 5; // x = 0b00000101 = 5y = x


113/443

g g ( )

If x is UNSIGNED (unsigned char in this case):

x = 250; // x = 0b11111010 = 250y = x >>2; // y = 0b00111110 = 62


Arithmetic Shift Right (Sign Extend)If x is SIGNED (char in this case):

x = -6; // x = 0b11111010 = -6

y = x >>2; // y = 0b11111110 = -2

OperatorsPower of 2 Integer Divide vs. Shift Right

If you are dividing by a power of 2, it will


114/443

usually be more efficient to use a right

shift instead


0 0 0 0

Works for integers or fixed point values

y = xy = x y = x ny = x n

1 0 1 0 >>

1010 510

0 0 0 0 0 1 0 1

Right Shift

OperatorsPower of 2 Integer Divide vs. Shift in MPLABC30

Example: Divide by 2 Example: Right Shift by 1

i ti t 2020 i ti t 2020


115/443

intint xx == 2020;;intint yy;;

yy == xx // 22;;


yy == xx >>>>11;;10: y = x / 2;10: y = x / 2;00288 804000 mov.w 0x0800,0x000000288 804000 mov.w 0x0800,0x00000028A 200022 mov.w 0x2 0x00040028A 200022 mov.w 0x2 0x0004

9: y = x >> 1;9: y = x >> 1;00282 804000 mov.w 0x0800,0x000000282 804000 mov.w 0x0800,0x000000284 DE8042 asr 0x0000 1 0x000000284 DE8042 asr 0x0000 1 0x0000

y = 10y = 10 y = 10y = 10


0028C 090011 repeat #170028C 090011 repeat #170028E D80002 div.sw 0x0000,0x00040028E D80002 div.sw 0x0000,0x0004

00290 884010 mov.w 0x0000,0x080200290 884010 mov.w 0x0000,0x0802

00286 884010 mov.w 0x0000,0x080200286 884010 mov.w 0x0000,0x0802

Example: Divide by 2 Example: Right Shift by 1

intint xx == 2020;;

OperatorsPower of 2 Integer Divide vs. Shift in MPLABC18

intint xx == 2020;;


116/443

10: y = x / 2;10: y = x / 2;

0132 C08C MOVFF 0x8c, 0x8a0132 C08C MOVFF 0x8c, 0x8a0134 F08A NOP0134 F08A NOP


yy == xx // 22;;9: y = x >> 1;9: y = x >> 1;0122 C08C MOVFF 0x8c, 0x8a0122 C08C MOVFF 0x8c, 0x8a0124 F08A NOP0124 F08A NOP


yy == xx >>>>11;;y = 10y = 10 y = 10y = 10


0136 C08D MOVFF 0x8d, 0x8b0136 C08D MOVFF 0x8d, 0x8b0138 F08B NOP0138 F08B NOP013A 0E02 MOVLW 0x2013A 0E02 MOVLW 0x2013C 6E0D MOVWF 0xd, ACCESS013C 6E0D MOVWF 0xd, ACCESS013E 6A0E CLRF 0xe, ACCESS013E 6A0E CLRF 0xe, ACCESS0140 C08A MOVFF 0x8a, 0x80140 C08A MOVFF 0x8a, 0x80142 F008 NOP0142 F008 NOP0144 C08B MOVFF 0x8b, 0x90144 C08B MOVFF 0x8b, 0x90146 F009 NOP0146 F009 NOP0148 EC6B CALL 0xd6, 00148 EC6B CALL 0xd6, 0

014A F000 NOP014A F000 NOP014C C008 MOVFF 0x8, 0x8a014C C008 MOVFF 0x8, 0x8a014E F08A NOP014E F08A NOP0150 C009 MOVFF 0x9, 0x8b0150 C009 MOVFF 0x9, 0x8b0152 F08B NOP0152 F08B NOP

0126 C08D MOVFF 0x8d, 0x8b0126 C08D MOVFF 0x8d, 0x8b0128 F08B NOP0128 F08B NOP012A 0100 MOVLB 0012A 0100 MOVLB 0

012C 90D8 BCF 0xfd8, 0, ACCESS012C 90D8 BCF 0xfd8, 0, ACCESS012E 338B RRCF 0x8b, F, BANKED012E 338B RRCF 0x8b, F, BANKED0130 338A RRCF 0x8a, F, BANKED0130 338A RRCF 0x8a, F, BANKED

1616--bit Shift on 8bit Shift on 8--bit Architecturebit Architecture

OperatorsMemory Addressing



117/443

SubscriptingSubscripting[][]

Address ofAddress of&&

IndirectionIndirection**

x[y]x[y]

&x&x

*p*p

TheThe yythth element of arrayelement of array xx

Pointer toPointer to xx

The object or function thatThe object or function thatpppoints topoints to


These operators will be discussed later in the sections onThese operators will be discussed later in the sections onarrays, pointers, structures, and unions. They are includedarrays, pointers, structures, and unions. They are includedhere for reference and completeness.here for reference and completeness.

Struct / UnionStruct / UnionMember byMember byReferenceReference

-->>

Struct / UnionStruct / Union

MemberMember

..

pp-->y>y

x.yx.y

The member namedThe member named yy in thein thestructure or union thatstructure or union thatpppoints topoints to

The member namedThe member named yy in thein the

structure or unionstructure or union xx

OperatorsOther



118/443

()()

sizeofsizeof

Function CallFunction Call

Size of anSize of an

foo(x)foo(x) Passes control to thePasses control to thefunction with thefunction with the

specified argumentsspecified arguments

sizeof xsizeof x The number of bytesThe number of bytes xx


(type)(type)

?:?:

,,

in bytesin bytes

Explicit typeExplicit type

castcast

ConditionalConditional

expressionexpression

SequentialSequential

evaluationevaluation

(short) x(short) x Converts the value ofConverts the value of xx

to the specified typeto the specified type

x ? y : zx ? y : z The value ofThe value of yy ifif xx is true,is true,else value ofelse value of zz

x, yx, y EvaluatesEvaluates xx thenthen yy, else, elseresult is value ofresult is value of yy

Syntax

OperatorsThe Conditional Operator

((t tt t ) ?) ? dd i fi f tt dd i fi f f lf l


119/443

Example

((t es tt es t -- ex prexp r) ?) ? dodo-- i fi f -- t r uet r ue:: dodo-- i fi f -- f a l s ef a l s e;;

intint xx == 55;;


5 is odd5 is oddResult:Result:

((xx %% 22 !=!= 00) ?) ?printfprintf(("%d is odd"%d is odd\\n"n",, xx) :) :printfprintf(("%d is even"%d is even\\n"n",, xx););

OperatorsThe Conditional Operator

The conditional operator may be used to

diti ll i l t i bl


120/443

Example 1 (most commonly used)

x = (c ondi t i on) ? a : b;

conditionally assign a value to a variable


x = a if condition is true

x = b if condition is false

Example 2 (less often used)

(c ondi t i on) ? (x = a):(x = b);

In both cases:

OperatorsThe Explicit Type Cast Operator

Earlier, we cast a literal to type float byt i it 4 0f


121/443

entering it as: 4.0f

We can cast the variable instead by usingthe cast operator: (t y pe)v ar i ab l e


Example: Integer Divide Example: Floating Point Divide

intint xx == 1010;;floatfloat yy;;

yy == xx // 44;;

intint xx == 1010;;floatfloat yy;;

yy == ((floatfloat))xx // 44;;

y = 2.y = 2.000000000000Because: int / intBecause: int / int intint

y = 2.y = 2.550000000000Because: float / intBecause: float / int floatfloat

OperatorsPrecedence

Operator Description Associativity

( )( ) Parenthesized ExpressionParenthesized Expression


122/443

pp

[ ][ ] Array SubscriptArray Subscript

.. Structure MemberStructure Member-->> Structure PointerStructure Pointer

LeftLeft--toto--RightRight


-- nary + annary + an os ve an ega ve gnsos ve an ega ve gns

++++ ---- Increment and DecrementIncrement and Decrement

! ~! ~ Logical NOT and Bitwise ComplementLogical NOT and Bitwise Complement

** Dereference (Pointer)Dereference (Pointer)

&& Address ofAddress of

sizeofsizeof Size of Expression or TypeSize of Expression or Type(type)(type) Explicit TypecastExplicit Typecast

RightRight--toto--LeftLeft

Continued on next slideContinued on next slide

OperatorsPrecedence


* / %* / % Multiply, Divide, and ModulusMultiply, Divide, and Modulus LeftLeft--toto--RightRight


123/443

p yp y

++ -- Add and SubtractAdd and Subtract

>> Shift Left and Shift RightShift Left and Shift Right

< => >= Greater Than and Greater Than or Equal ToGreater Than and Greater Than or Equal To






&&&& Logical ANDLogical AND

|||| Logical ORLogical OR

?:?: Conditional OperatorConditional Operator




== !=== != Equal To and Not Equal ToEqual To and Not Equal To

&& Bitwise ANDBitwise AND^ Bitwise XORBitwise XOR

|| Bitwise ORBitwise OR

Continued on next slideContinued on next slide





OperatorsPrecedence


== AssignmentAssignment


124/443

+=+= --== Addition and Subtraction AssignmentsAddition and Subtraction Assignments

/= *=/= *= Division and Multiplication AssignmentsDivision and Multiplication Assignments

%=%= Modulus AssignmentModulus Assignment

== Shift Left and Shift Right AssignmentsShift Left and Shift Right Assignments



&= |=&= |= Bitwise AND and OR AssignmentsBitwise AND and OR Assignments

^=^= Bitwise XOR AssignmentBitwise XOR Assignment

,, Comma OperatorComma Operator LeftLeft--toto--RightRight

Operators grouped together in a section havethe same precedence conflicts within a sectionare handled via the rules of associativity

OperatorsPrecedence

When expressions contain multiple

operators their precedence determines


125/443

Expression Effective Expression

operators, their precedence determines

the order of evaluation


a + ++ba + ++b a + (++b)a + (++b)a + ++b * ca + ++b * c a + ((++b) * c)a + ((++b) * c)

If functions are used in an expression, there is no set order ofIf functions are used in an expression, there is no set order of

evaluation for the functions themselves.evaluation for the functions themselves.

e.g.e.g. x = f() + g()x = f() + g()There is no way to know ifThere is no way to know if f()f() oror g()g() will be evaluated first.will be evaluated first.

If two operators have the same

precedence their associativity determines

OperatorsAssociativity


126/443

precedence, their associativity determines

the order of evaluationExpression Effective ExpressionAssociativity


You can rely on these rules, but it is goodprogramming practice to explicitly group

elements of an expression

-- --

x = y = zx = y = z x = (y = z)x = (y = z)RightRight--toto--LeftLeft~++x~++x ~(++x)~(++x)RightRight--toto--LeftLeft


127/443


Lab Exercise 4

Operators

Lab 04Operators


O th l b PCO th l b PC


128/443







in MPLAB IDE, close it byin MPLAB IDE, close it by

selectingselecting Close WorkspaceClose Workspace fromfromthethe FileFile menu before opening amenu before opening anew one.new one.

Lab 04Operators

/*###########################################################################

Solution: Steps 1 and 2


129/443

# STEP 1: Add charVariable1 to charVariable2 and store the result in

# charVariable1. This may be done in two ways. One uses the# ordinary addition operator, the other uses a compound assignment

# operator. Write two lines of code to perform this operation# twice - once for each of the two methods.

# Don't forget to end each statement with a semi-colon!

*

2010 Microchip Technology Incorporated. All Rights Reserved.Slide 1291421 CPL

//Add using addition operator

charVariable1 = charVariable1 + charVariable2;//Add using compound assignment operator

charVariable1 += charVariable2;

/*###########################################################################

# STEP 2: Increment charVariable1. There are several ways this could be

# done. Use the one that requires the least amount of typing.

###########################################################################*/

//Increment charVariable1

charVariable1++;

Lab 04Operators

/*###########################################################################

Solution: Steps 3 and 4


130/443

# STEP 3: Use the conditional operator to set longVariable1 equal to

# intVariable1 if charVariable1 is less than charVariable2.# Otherwise, set longVariable1 equal to intVariable2

# NOTE: The comments below are broken up into 3 lines, but the code you# need to write can fit on a single line.

###########################################################################*/

2010 Microchip Technology Incorporated. All Rights Reserved.Slide 1301421 CPL

//If charVariable1 < charVariable2, then

//longVariable1 = intVariable1, otherwise

//longVariable1 = intVariable2longVariable1 = (charVariable1 < charVariable2) ? intVariable1 : intVariable2;

/*###########################################################################

# STEP 4: Shift longVariable2 one bit to the right. This can be accomplished

# most easily using the appropriate compound assignment operator.

###########################################################################*/

//Shift longVariable2 one bit to the right

longVariable2 >>= 1;

Lab 04Operators

/*###########################################################################

Solution: Step 5


131/443

/ ###########################################################################

# STEP 5: Perform the operation (longVariable2 AND 0x30) and store the result# back in longVariable2. Once again, the easiest way to do this is

# to use the appropriate compound assignment operator that will# perform an equivalent operation to the one in the comment below.

###########################################################################*/


//longVariable2 = longVariable2 & 0x30

longVariable2 &= 0x30;

Lab 04Conclusions

Most operators look just like their normal

mathematical notation


132/443

mathematical notation

C adds several shortcut operators in theform of compound assignments


Most C programmers tend to use the

shortcut operators


133/443


Expressions and

Statements

Expressions

Represents a single data item (e.g.

h t b t )


134/443

character, number, etc.)

May consist of:


A single entity (a constant, variable, etc.)

A combination of entities connected by

operators (+, -, *, / and so on)

Example

ExpressionsExamples

aa ++bb


135/443

xx == yyspeedspeed == distdist//timetime


zz == ReadInputReadInput()()

cc


136/443

Three kinds of statements in C:

Ex ression Statements


Compound StatementsControl Statements

Expression Statements

An expression followed by a semi-colon

Execution of the statement causes the


137/443

Examples

Execution of the statement causes the

expression to be evaluated


ii == 00;;

ii++;++;aa == 55 ++ ii;;yy = (= (mm ** xx) +) +bb;;

printf(printf("Slope = %f""Slope = %f", m, m););;;

Compound Statements

A group of individual statements enclosed

within a pair of curly braces { and }


138/443

within a pair of curly braces { and }

Individual statements within may be any


,

Allows statements to be embedded withinother statements

Does NOT end with a semicolon after }Also called Block Statements

Example

Compound StatementsExample

{{flfl fi i hfi i h


139/443

floatfloat startstart,, finishfinish;;

startstart == 0.00.0;;


finishfinish == 400.0400.0;;

distancedistance == finishfinish startstart;;timetime == 55.255.2;;speedspeed == distancedistance // timetime;;

printfprintf(("Speed = %f m/s""Speed = %f m/s",, speedspeed););}}

Control Statements

Used for loops, branches and logical tests

Often require other statements embedded


140/443

Example

q

within them


whilewhile ((distancedistance


141/443


Making Decisions

C has no Boolean data type

Boolean expressions return integers:

Boolean Expressions


142/443

p g

0 if expression evaluates as FALSENon-zero if expression evaluates as TRUE


(usually returns 1, but this is not guaranteed)

intintmainmain((voidvoid)){{

intint xx == 55,, yy,, zz;;

yy = (= (xx >>44););zz = (= (xx >>66););whilewhile ((11););

}}

y = 1 (TRUE)y = 1 (TRUE)z = 0 (FALSE)z = 0 (FALSE)

Boolean ExpressionsEquivalent Expressions

If a variable, constant or function call isused alone as the conditional expression:


143/443

(MyVar) or (Foo())

This is the same as saying:


(MyVar != 0) or (Foo() != 0)

In either case, ifMyVar 0 or Foo()0,then the expression evaluates as TRUE

(non-zero)

C Programmers almost always use the

first method (laziness always wins in C)

Syntax

if Statement

ifif ((ex pr es s i onex pr es s i on))s t at ements t at ement


144/443

ex pr es s i onis evaluated for booleanTRUE (0) or FALSE (=0)


Note

If TRUE, then s t at ement is executed

if (ex pr es s i on){

s t at ement1s t at ement2

}

Whenever you sees t at ement in a

syntax guide, it may be replaced by a

compound (block) statement.

Remember: spaces and new lines are

not significant.

Syntax

if StatementFlow Diagram

ifif ((ex pr es s i onex pr es s i on))s t at ements t at ement


145/443


TRUE

FALSEex pr es s

programacion en c para pic mplaide

Documents