13878_C-Language (All Concepts)

8/8/2019 13878_C-Language (All Concepts)

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C Programming BasicsC Programming Basics Introduction to C Data types in C Variables Type conversions Standard input/output

Arithmetic, relational, logical operators Header files and libraries Loops and decisions Scope of variables Strings

Functions, call by value, call by reference Arrays Structures Unions

Pointers Files


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History of CHistory of C--LanguageLanguage Developed by Dennis M.Ritchie and BrianDeveloped by Dennis M.Ritchie and Brian

Kernighan of AT&T Bell Labs in 1972Kernighan of AT&T Bell Labs in 1972

In 1983 the American National StandardsIn 1983 the American National StandardsInstitute began the standardisation processInstitute began the standardisation process

In 1989 the International StandardsIn 1989 the International StandardsOrganisation continued the standardisationOrganisation continued the standardisation

processprocess

In 1990 a standard was finalised, knownIn 1990 a standard was finalised, knownsimply as Standard Csimply as Standard C


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Why teach C?Why teach C? C isC is smallsmall (only 32 keywords).(only 32 keywords).

C isC is commoncommon (lots of C code about).(lots of C code about).

C isC is stablestable (the language doesnt change much).(the language doesnt change much).

C isC is quick runningquick running..

C is theC is the basis for many other languagesbasis for many other languages (Java, C++,(Java, C++,

awk, Perl).awk, Perl). It may not feel like it but C is one of the easiestIt may not feel like it but C is one of the easiest

languages to learn.languages to learn.

NOTE: Obviously programmers will find this courseNOTE: Obviously programmers will find this course

easier than everyone else. BUT, this course is for noneasier than everyone else. BUT, this course is for non--programmers. If you cannot understand what I say,programmers. If you cannot understand what I say,please please ask me either in the lecture orplease please ask me either in the lecture orafterwards.afterwards.


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Why use C?Why use C? C is not "safe"C is not "safe"

It assumes you know what you're doingIt assumes you know what you're doing

It has a lot of scope for bugsIt has a lot of scope for bugs

It's a good systems programmingIt's a good systems programminglanguagelanguage

Not much is hiddenNot much is hidden Faster than Java, more predictableFaster than Java, more predictable

performanceperformance

It has all the lowIt has all the low--level operationslevel operations


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Strengths:

C-Language

Weaknesses:

1. Efficiency

2. Portability

3. Power

4. Flexibility

5. Standard library

6. Integration with UNIX

1. C programs can be error-prone

2. C programs can be difficult to understand

3. C programs can be difficult to modify


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The Benefits And Pitfalls Of CThe Benefits And Pitfalls Of C

BenefitsBenefits Its a powerful language (doesnt restrictIts a powerful language (doesnt restrict

you)you)

FastFastA practical language (real applications)A practical language (real applications)

PitfallsPitfalls

Its a powerful language (No programmerIts a powerful language (No programmerfailfail--safes)safes)

Compiled code is not portableCompiled code is not portable


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Structured ProgrammingStructured Programming C, Pascal, Fortran areC, Pascal, Fortran are proceduralprocedural programming languages.programming languages. A program in a procedural language is a list of instructions,A program in a procedural language is a list of instructions,

augmented with loops and branches.augmented with loops and branches.

For small programs no other organizational principleFor small programs no other organizational principle(paradigm) is needed.(paradigm) is needed.

Larger programs are broken down into smaller units.Larger programs are broken down into smaller units.

A procedural program is divided intoA procedural program is divided into functionsfunctions, such that, such thatideally each has clearly defined purpose and interface toideally each has clearly defined purpose and interface toother functions.other functions.

The idea of breaking a program into functions can beThe idea of breaking a program into functions can befurther extended by grouping functions that performfurther extended by grouping functions that performsimilar tasks intosimilar tasks into modulesmodules..

Dividing a program into functions and modules is the keyDividing a program into functions and modules is the keyidea ofidea of structured programmingstructured programming..


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Compiling and Linking

1. Preprocessing. The program is first given to a preprocessor,

which obeys commands that begin with # (known as directives).

#include (include the info in before compiling)

test.c ---> (compiled) ---> test.obj (linked) ---> executable file

2. Compiling. The modified program now goes to a compiler,which translates it into machine instructions (object code).

3. Linking. A linker combines the object code produced by the

compiler with any additional code needed to yield a complete

executable program.


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Some programmer jargonSome programmer jargon

Source code:Source code: The stuff you type into the computer. TheThe stuff you type into the computer. Theprogram you are writing.program you are writing.

Compile (build):Compile (build): Taking source code and making a programTaking source code and making a programthat the computer can understand.that the computer can understand.

Executable:Executable: The compiled program that the computer can run.The compiled program that the computer can run.

Language:Language: (Special sense) The core part of C central to writing(Special sense) The core part of C central to writingC code.C code.

Library:Library:Added functions for C programming which are bolted onAdded functions for C programming which are bolted on

to do certain tasks.to do certain tasks. Header file:Header file: Files ending in .h which are included at the start ofFiles ending in .h which are included at the start of

source code.source code.


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Contd.Contd.

Compiler:Compiler: Translates program written in "source"Translates program written in "source"

language to "target" languagelanguage to "target" language

Interpreter:Interpreter: Translate and immediately executeTranslate and immediately execute

Assembler:Assembler:

Translate into machine language forTranslate into machine language forparticular machineparticular machine

MacroProcessor:MacroProcessor:

Textual substitutionsTextual substitutions


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Keywords

In Standard C, the keywords in Table 2.1 have special significanceto the compiler and therefore can not be used as identifiers.

Table 2.1 - Keywords

auto double int struct

break else long switch

case enum register typedef

char extern return union

const float short unsignedcontinue for signed void

default goto sizeof volatile

do if static while


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The Format of CThe Format of C

Statements are terminated with semicolonsStatements are terminated with semicolons Indentation is ignored by the compilerIndentation is ignored by the compiler

C is case sensitiveC is case sensitive -- all keywords and Standardall keywords and StandardLibrary functions are lowercaseLibrary functions are lowercase

Strings are placed in double quotesStrings are placed in double quotes

Newlines are handled viaNewlines are handled via \\nn

Programs are capable of flagging success orPrograms are capable of flagging success or

error, those forgetting to do so have one orerror, those forgetting to do so have one orother chosenother chosen randomly!randomly!


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VariablesVariables

Variables must be declared before useVariables must be declared before useimmediately after {immediately after {

Valid characters are letters, digits and _Valid characters are letters, digits and _

First character cannot be a digitFirst character cannot be a digit

31 characters recognised for local variables31 characters recognised for local variables(more can be used, but are ignored)(more can be used, but are ignored)

Some implementations recognise only 6Some implementations recognise only 6

characters in global variables (and functioncharacters in global variables (and functionnames)!names)!

Upper and lower case letters are distinctUpper and lower case letters are distinct


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printfprintf andandscanfscanfprintfprintf writeswrites integervalues to screen whenintegervalues to screen when%iisused%iisused

scanfscanf readsreads integervalues from theintegervalues from the

keyboardwhen %i isusedkeyboardwhen %i isused

& VERY important with& VERY important with scanfscanf (required to(required tochangechange the parameter, this will bethe parameter, this will beinvestigated later)investigated later) -- absence will makeabsence will makeprogram very illprogram very ill

& not necessary with& not necessary with printfprintf becausebecause

current value of parameter is usedcurrent value of parameter is used


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The Basic Structure Of A C ProgramThe Basic Structure Of A C Program

example_program.c

int

main ()

{

}

Global variables

Local variables

/* Program documentation */

#Preprocessor directives

Function prototypes

Function definitions

Global constants


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Hello World ProgramHello World Program

#include // input#include // input--output libraryoutput library

int main()int main() // function main// function main

{{

printf(Hello Worldprintf(Hello World\\n); // send string to standard outputn); // send string to standard outputreturn 0;return 0;

}}

Compile the source file helloworld.c with the commandCompile the source file helloworld.c with the commandgcc helloworld.cgcc helloworld.c o helloworldo helloworld


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Hello World ProgramHello World Program#include #include

includes the standard I/O library which allows you to read from theincludes the standard I/O library which allows you to read from thekeyboard (standard in) and write to the screen (standard out)keyboard (standard in) and write to the screen (standard out)

int main()int main()

declares the main function. Every Cdeclares the main function. Every C--program must have a functionprogram must have a functionnamed main somewhere in the codenamed main somewhere in the code

{ ... }{ ... }

The symbols { and } mark the beginning and end of a block of code.The symbols { and } mark the beginning and end of a block of code.

printf(Hello Worldprintf(Hello World\\n)n)

Sends output to the screen. The portion in quotes ... is the formatSends output to the screen. The portion in quotes ... is the format

strings and describes how the data is formatted.strings and describes how the data is formatted.return 0;return 0;

This causes the function main to return an error code of 0 (no error)This causes the function main to return an error code of 0 (no error)to the shell that started the program.to the shell that started the program.


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Compilation & LinkingCompilation & Linking

helloworld.cstdio.h

#include

helloworld.o

helloworld

header file

compiler

linker

executable file

object file

source file


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Variable DeclarationVariable Declarationint b;int b;

double x;double x;

unsigned int a;unsigned int a;

char c;char c;

C is a typed language that means a variable has aC is a typed language that means a variable has a namename

typetype

C standard typesC standard types

int, double, char, float, short, long, long doubleint, double, char, float, short, long, long double unsigned char, unsigned short, unsigned int,unsigned char, unsigned short, unsigned int,

unsigned longunsigned long


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Primitive DataPrimitive Data--TypesTypes

integer data-types :char, short, int, long, unsigned char, unsigned short,

floating point data-types :

float, double, long double character data-type :charcharacter constants in single quotes : a, \n


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Primitive DataPrimitive Data--TypesTypesTypeType LowLow HighHigh Digits of Digits of

PrecisionPrecisionBytesBytes

charchar --128128 127127 -- 11

shortshort --3276832768 3276732767 -- 22intint --21474836482147483648 21474836472147483647 -- 22

longlong --21474836482147483648 21474836472147483647 -- 44

floatfloat 3.4x103.4x10--3838 3.4x103.4x103838 77 44

doubledouble 1.7x101.7x10--308308 1.7x101.7x10308308 1515 88

longlongdoubledouble

3.4x103.4x10--49324932 3.4x103.4x1049324932 1919 1010


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Variable DefinitionsVariable Definitions

int a;double x = 5.9;

char answer = n;

double y=x;

A declaration introduces a variables name into aprogram and specifies its type A definition is a declaration which also sets asidesmemory for that variable (which is usually the case)

In C it is possible to initialize a variable at the sametime it is defined, in the same way one assigns a valueto an already defined variable.

Examples of variable definitions:


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ConstantsConstants constants can be specified using the preprocessordirective #define

example:#define PI 3.14159

the preprocessor replaces the identifier PI by the text

3.14159 throughout the program the major drawback of #define is that the data type ofthe constant is not specified

the preprocessor merely replaces all occurences of thestring PI with 3.14159

CONVENTION: reserve CAPITAL letters for constants and usesmall caps for variables and functions


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CommentsComments comments are always a good thing to use because

not everyone is as smart as you are and needs moreexplanation in order to understand your program

you may not be as smart next month when you have

to change your program comments should clarify your code and explain therational behind a group of statements

comment syntax (C style) /* *//* this is a comment

which can go across multiplelines of code */


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Type ConversionsType Conversions

double pi=3.14;

char c=x;

C is a hard-typed language, meaning that each variable hasa fixed type that does not change and which determines thepossible assignments and applicable operators

Some type conversions occur automatically for example intto float or float to double, but also char to intint i = 17;

float x = i; /* assigns 17 to x */

int j = 2;

float y = i/j; /* assigns 17/2 = 8 to y not 8.5 */ Type conversions can be forced by a programmer througha type castfloat z = (float) i / j; /* casts i into float before division */


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Library FunctionsLibrary Functions Many functionalities in C are carried out by library functions. These functions perform file access, data conversion andmathematical computations.

#include /* include header file for math functions */

int main(){

double x;

double y;

y=1.57;x=sin(y);

}


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Header FilesHeader Files a header file contains the declaration of functions

you want to use in your code the preprocessor directive #include takes care ofincorporating a header file into your source file

example:#include

#include myprog.h

the brackets indicate that the compiler first searchesthe standard include directory which contains thestandard C header files first

the quotation marks indicate that the compiler first searchesfor header files in the local directory if you do not include the appropriate header file

you get an error message from the compiler


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Header and Library FilesHeader and Library Files

myprog.cmath.h

myprog.h

#include

#include myprog.h

myprog.o

myprog

libm.a

user header file

compiler

linker

library header file

library fileobject file

executable file


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Input / OutputInput / Output/*Program for print the different data types*//*Program for print the different data types*/

#include #include int main()int main()

{{

int a;int a;

double x;double x;

char c;char c;printf(Enter integer:);printf(Enter integer:);

scanf(%d,&a);scanf(%d,&a);

printf(printf(\\nEnter double:);nEnter double:);

scanf(%lf,&x);scanf(%lf,&x);

printf(printf(\\nEnter character:);nEnter character:);

scanf(%c,&c);scanf(%c,&c);printf(printf(\\nThe value of a is %d, of x is %lf, of c is %cnThe value of a is %d, of x is %lf, of c is %c\\n,a,x,c);n,a,x,c);

}}


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Input / OutputInput / Output A stream isan abstraction thatrefers to a flow of data.

standardoutput

device

stdout variable aprintf(%d,a);

standardinput

device

stdin variable ascanf(%d,&a);


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Input / OutputInput / Output

printf allows you to send output to standard out (screen)printf allows you to send output to standard out (screen)

The special character The special character \\n represents carriage return line feedn represents carriage return line feed The symbol %d is a placeholder for an integer variable in theThe symbol %d is a placeholder for an integer variable in the

format stringformat string

printf(the value of a is %dprintf(the value of a is %d\\n,a)n,a)

that will be replaced by the value of the variable a when thethat will be replaced by the value of the variable a when the

printf statement is executedprintf statement is executed Placeholders:Placeholders:

integer %dinteger %d

long %ldlong %ld

float %ffloat %f

double %lfdouble %lf

char %cchar %c

string %sstring %s


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Input / OutputInput / Output

scanf allows you to read input from standard inscanf allows you to read input from standard in

(keyboard)(keyboard) scanf uses the same placeholders as printfscanf uses the same placeholders as printf

scanf (%d,&a)scanf (%d,&a)

the program reads an integer value from thethe program reads an integer value from thekeyboard and places its value into the integerkeyboard and places its value into the integervariable avariable a

Notice to put an & in front of the variable, theNotice to put an & in front of the variable, the

reason becomes clear when you learn morereason becomes clear when you learn moreabout pointersabout pointers


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Arithmetic andIncrement OperatorsArithmetic andIncrement Operators

int a=4;int a=4;int b=3;int b=3;

b=b+a;b=b+a;

b+=3; /* arithmetic assignment operator,b+=3; /* arithmetic assignment operator,same as b=b+3 */same as b=b+3 */

a++; /* increment operator, same as a=a+1;a++; /* increment operator, same as a=a+1;

*/*/a=b++, /* postfix operator */a=b++, /* postfix operator */

a=3 * ++b; /* prefix operator */a=3 * ++b; /* prefix operator */


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Arithmetic OperatorsArithmetic Operators

multiplication, summation, subtraction, divisionint i = 1/3; /* integer division result 0 */float x = 1.0/3; /* floating point division result 0.3333 */

int j = 7 % 3; // modulo operator remainder of 7/3

prefix and postfix-increment operator ++

int i=3;int j=7;

printf(%d,10 * i++); /* outputs 30, i has value 4 afterwards */

Printf(%d,10 * ++j); /* outputs 80, j has value 8 afterwards */

arithmetic assignment operatorsfloat x=6.0;

x+=3.5;

is equivalent tox=x+3.5;


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Relational OperatorsRelational Operators

In C there is no special boolean type. InsteadIn C there is no special boolean type. Insteadint is used for boolean expression with theint is used for boolean expression with theconvention that 0 is false, everything else isconvention that 0 is false, everything else istrue.true.

Relational operatorsRelational operators > greater> greater < less< less >= greater or equal>= greater or equal


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Relational OperatorsRelational Operators

a relational operator compares two values of primitivein data types such as char, int, float

typical relationships are equal to, less than and greater than the result of a comparison is either true or false, where 0 is

false and any value different from 0 is true C provides the following relational operators

, ==, !=, = example:

int x=44;int y=12;

(x == y) /* false */

(x >= y) /* true */

(x != y) /* true */


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increment expression

test expression

initialization expression

a loop causes a section of the program to be repeatedmultiple times while the loop condition remains true

C knows three kinds of loops for loop

while loop do loop the for loop repeats a code segment a fixed number of times the for statement contains three expressions usually

refering to the same loop variable separated by semicolons

LoopsLoops

for ( i=0; i


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For LoopFor Loop

increment expressiontest expressioninitialization expression

for ( i=0; i


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For LoopFor Loop

#include #include


{{

int a;int a;

int i;int i;

a=1;a=1;

for (i=0;i


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For LoopFor Loopfor (i=0; i


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For LoopFor Loop#include #include


{{

int number;int number;

int i;int i;

long fact;long fact;

fact=1;fact=1;

printf(Enter number:);printf(Enter number:);

scanf(%d,&number);scanf(%d,&number);

for (i=number; i>0; ifor (i=number; i>0; i----))fact*=i;fact*=i;

printf(Factorial of %d is %ldprintf(Factorial of %d is %ld\\n,number,fact);n,number,fact);

}}


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Indendation and Loop StyleIndendation and Loop Style it is good programming practice to indent loops there is some variation of the style used for loops

whatever style you use do it consistently

for (i=0; i


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While / DoWhile / Do--While LoopWhile Loop

while (a>b)while (a>b){{

}}

the body of the loop is executed as long as the testthe body of the loop is executed as long as the teststatement is true (possibly zero times)statement is true (possibly zero times)

dodo

{{

} while (a>b);} while (a>b);

the body of the loop is executed and then repeated asthe body of the loop is executed and then repeated aslong as the test statement is true (at least once)long as the test statement is true (at least once)


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While LoopWhile Looptest expressionwhile ( c != y )

{

}

body of loop

testexpression exit

true

false


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While LoopWhile Loop#include #include


{{

int number;int number;

int i;int i;

long factlong fact

fact=1;fact=1;

printf(Enter number:);printf(Enter number:);

scanf(%d,&number);scanf(%d,&number);

i=number;i=number;while (i>0)while (i>0)

fact*=ifact*=i----;;

printf(Factorial of %d is %ldprintf(Factorial of %d is %ld\\n,number,fact);n,number,fact);

}}


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While LoopWhile Loop

the while loop is used when the number of iterationsis unknown before the loop is started

the while loop is repeated as long as the test expressionremains true

char c=n;

while ( c != y)

{

printf(Do you want to continue: (y/n)\n);scanf(%c,&c);

}


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Do LoopDo Loop

test expressiondo{ }

while ( c != y );

body of loop

testexpression exit

true

false


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DoDo -- While LoopWhile Loop#include #include


{{

i=number;i=number;dodo

{{

fact*=ifact*=i----;;

} while (i>0); /* do not forget the semicolon */} while (i>0); /* do not forget the semicolon */printf(Factorial of %d is %ldprintf(Factorial of %d is %ld\\n,number,fact);n,number,fact);

}}


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Do LoopDo Loop

in the do loop the test expression is evaluated at theend of the loop, therefore the body is executed atleast once

char c;

do

{

printf(Do you want to continue: (y/n)\n);

scanf(%c,&c);}

while ( c != y);


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If Else StatementIf Else Statement

test expressionif ( x > 100){

}

else{

}

body of if

testexpression

exit

true

false

body of else


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If Else StatementIf Else Statement

depending on whether the test condition is true or falseeither the if or the else branch is executed

int x;

Printf(Enter a number: );Scanf(%d,&x);

if ( x > 100)

printf(%d is greater than 100\n,x);

else

printf(%d is smaller or equal than 100\n,x);


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IfElse StatementIfElse Statement#include #include int main()int main()

{{

int a,b;int a,b;

scanf(%d %d,&a,&b);scanf(%d %d,&a,&b);if (a>b)if (a>b)

printf(%d is larger than %dprintf(%d is larger than %d\\n,a,b);n,a,b);

elseelse

if (a==b)if (a==b)printf(%d is equal to %dprintf(%d is equal to %d\\n,a,b);n,a,b);

elseelse

printf(%d is smaller than %dprintf(%d is smaller than %d\\n,a,b);n,a,b);

}}


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IfElse StatementIfElse Statement

if (a>b)if (a>b){{

}}

elseelse

{{

}}

the if part is executed if the test statement isthe if part is executed if the test statement istrue, otherwise the else part is executed.true, otherwise the else part is executed.


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Nested IfElse StatementNested IfElse Statementif (a>b)if (a>b){{

if (b>c)if (b>c)

printf(sorted = %d %d %dprintf(sorted = %d %d %d\\n,a,b,c);n,a,b,c);

elseelse

if (a>c)if (a>c)

printf(sorted = %d %d %dprintf(sorted = %d %d %d\\n,a,c,b);n,a,c,b);

elseelse

printf(sorted = %d %d %dprintf(sorted = %d %d %d\\n,c,a,b);n,c,a,b);

}}

elseelse

{{if (a>c)if (a>c)

printf(sorted = %d %d %dprintf(sorted = %d %d %d\\n,b,a,c);n,b,a,c);

elseelse


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Logical OperatorsLogical Operators

logical and : &&(x >= 5) && ( x

if (alpha < beta)min = alpha;

else

min = beta;

min = (alpha


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Switch StatementSwitch Statement

variableequalsconst 1

exit

true

false

first case body

variableequals

const 2

true

false

second case body

default body


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Switch StatementSwitch Statement the switch statement is used if there are more thantwo alternatives and the decision depends on the valueof the same variable

the switch statement can replace a ladder of multiplenested if..else statements

switch()

{

case :

break;case :

break;

default :

}


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Switch StatementSwitch Statement

char c;

printf(Enter your choice (a/b/c) : );

Scanf(%c,&c);

switch (c)

{

case a:printf(You picked a!\n);

break;

case b:

printf(You picked a!\n);

break;

case c:

printf(You picked a!\n);

break;

default:

printf(You picked neither a,b,c !\n);

}


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Scope of VariablesScope of Variables a block is a section of code delimited by a pair

of brackets { }

a declaration introduces a variable into a scope( a specific part of program text)

the scope of a variable is the block within whichthe variable is declared

a variable declared outside a function is global.

a declaration of a variable in an inner block can hidea declaration in an enclosing block or a global variable


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lifetime of outer i

visibility of outer i

Scope of VariablesScope of Variables

int i; /* global variable */

int main()

{int i=3; /* local variable */

{

int j=5; /* local variable */

int i=7; /* local i hides outer i */

printf(%d\n i); /* outputs 7 */} /* end of scope of j and inner i */

printf(%d\n i); /* outputs 3 */

} /* end of scope of outer i */


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CharactersCharacters

TypeType charchar

Characters are small integers (0Characters are small integers (0--255)255)

Character constants are integers thatCharacter constants are integers thatdenote corresponding charactersdenote corresponding characters

'0','1','A','B','a','b',''0','1','A','B','a','b','\\nn

''

ASCII code maps characters to integersASCII code maps characters to integers


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ASCII CodeASCII Code

00 11 22 33 44 55 66 77 88 99

4848 4949 5050 5151 5252 5353 5454 5555 5656 5757

AA BB CC DD EE FF GG HH II JJ

6565 6666 6767 6868 6969 7070 7171 7272 7373 7474

aa bb cc dd ee ff gg hh ii jj

9797 9898 9999 100100 101101 102102 103103 104104 105105 106106

NULLNULL((\\0)0)

BELBEL((\\g)g)

TABTAB((\\t)t)

NEWLINENEWLINE((\\n)n)

SPACESPACE

00 77 99 1010 3232

S iS i


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StringsStrings

String is collection of Characters (or )String is collection of Characters (or )group of elements.group of elements.

Character arrays that are NULLCharacter arrays that are NULL

terminated.terminated.ExampleExample

char arr[4] = hi;char arr[4] = hi;

hh i i NULNULLL

??

[0] [1] [2] [3]


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StringsStrings

Two interpretationsTwo interpretations Arrays whose elements are charactersArrays whose elements are characters

Pointers pointing to charactersPointers pointing to characters

Strings are always terminated with a NULLStrings are always terminated with a NULLcharacter ('character ('\\0' or 0)0' or 0)

char a[]="hellochar a[]="hello\\n"; /* size? */n"; /* size? */

char* b=hellochar* b=hello\\n;n;

olleh \n null

*b

111108108101104 10 0

*(b+1) *(b+2) *(b+3) *(b+4) *(b+5) *(b+6)a[0] a[1] a[2] a[3] a[4] a[5] a[6]


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String InitializationString Initialization

InitializationInitialization

char m[char m[99] = I like C;] = I like C;

char m[ ] = I like C;char m[ ] = I like C;

char m[] = { I, , l, i, k, e, ,C };char m[] = { I, , l, i, k, e, ,C };

I l i k e C \0

m[0] m[1] m[2] m[3] m[4] m[5] m[6] m[7] m[8]


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char s[char s[3030] = "c programming "; // ok, preferred] = "c programming "; // ok, preferred

char s[char s[3030] = {"c programming "}; // ok, redundant] = {"c programming "}; // ok, redundant

char s[char s[3030] = {c programming }; // illegal] = {c programming }; // illegalchar s[char s[3030] = {c,p,i};] = {c,p,i}; // illegal// illegal

char s[char s[3030] = {S',I',I',T'}; // ok, inconvenient] = {S',I',I',T'}; // ok, inconvenient

char string_var[char string_var[3030];]; // ok, not initialize// ok, not initialize

char* s = c++; //s[char* s = c++; //s[00]=c,s[]=c,s[11]=+,s[]=+,s[22]=+, s[]=+, s[33]=]=00; // ok, initialize; // ok, initializechar str[char str[2020] = Initial value; // ok, initialize] = Initial value; // ok, initialize

tI n i i

va l a \0l u e ?

?? ? ? ?

Null character

String InitializationString Initialization


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Null is the end of itNull is the end of it

#include #include

#include #include

#include #include

#include #include


{{

char x[ ];char x[ ];

strcpy(x,"Snoopy is not a cat");strcpy(x,"Snoopy is not a cat");

x[x[1111] = '] = '\\00';';

printf("x = %s",x);printf("x = %s",x);

getch();getch();

}}


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char s[char s[55]="SIIT";]="SIIT";

char dept[char dept[55], *d=dept;], *d=dept;

char name[char name[2020]];;

name = name = Peter PanPeter Pan"";;

strcpy(name,strcpy(name,Peter PanPeter Pan")");;strcpy(dept,"IT");strcpy(dept,"IT");

printf("%s %s %sprintf("%s %s %s\\n",d,s,dept);n",d,s,dept);

d = strcpy(s,"EE");d = strcpy(s,"EE");

printf("%s %s %s %sprintf("%s %s %s %s\\n",name,d,s,dept);n",name,d,s,dept);

char cchar c11[[3030], c], c22[[3030]=This is new c]=This is new c11 string;string;

char s[char s[3030] = "c programming ";] = "c programming ";char strchar str11[[3030]];;

char *str;char *str;

strcpy(cstrcpy(c11, c, c22));;

str = strcat(s,"is great!!");str = strcat(s,"is great!!");

strstr11 = strcat(s,"is great!!");= strcat(s,"is great!!");

Make sure that you haveMake sure that you have

enough memory space toenough memory space to

assign the string,assign the string,

otherwise some chars willotherwise some chars will

be lost.be lost.

String AssignmentString Assignment


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InIn--Class ExampleClass Example

void main()void main()

{{ char first[100], last[100];char first[100], last[100];

int i;int i;

strcpy(first,"Peter");strcpy(first,"Peter");

sprintf(last, "Pan");sprintf(last, "Pan");

printf("my name is %s, %sprintf("my name is %s, %s\\n", last, first);n", last, first);

for (i=0; i


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FunctionsFunctions

a function groups a number of program statementsinto a unit and gives it a name

the function can be invoked from other parts of the program dividing a program into functions is one way to structure

your program (structured programming)

a function declaration specifies the name of the functionthe type of the value returned and the number andtype of arguments that must be supplied in a call ofthe function

a function definition contains the body of the function

typically function declarations take place in header files (.h)whereas the function definitions are stored in sourcefiles (.c)

h i f ih i f i


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What is a function?What is a function?

TheThe functionfunction is one of the most basic thingsis one of the most basic thingsto understand in C programming.to understand in C programming.

AA functionfunction is a subis a sub--unit of a program whichunit of a program whichperforms a specific task.performs a specific task.

We have already (without knowing it) seen

We have already (without knowing it) seenone function from the C libraryone function from the C library printf.printf.

We need to learn to write our own functions.We need to learn to write our own functions.

Functions takeFunctions take argumentsarguments (variables) and(variables) and

may return anmay return an argument.argument. Think of a function as extending the CThink of a function as extending the C

language to a new task.language to a new task.

A l f tiA l f ti


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An example functionAn example function#include

int maximum (int, int); /* Prototype see later in lecture */

int main(int argc, char*argv[]){

int i= 4;int j= 5;

int k;k= maximum (i,j); /* Call maximum function */

printf ("%d is the largest from %d and %d \n",k,i,j);printf ("%d is the largest from %d and %d \n",maximum(3,5), 3, 5);return 0;

}

int maximum (int a, int b)/* Return the largest integer */

{

if (a > b)return a; /* Return means "I am the result of the function"*/

return b; /* exit the function with this result */}

Prototype the function

Call the function

The function itself

function header


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Factorial program (and thoughts)Factorial program (and thoughts)int main()

{

int number=4;

int answer;

int count;

answer=1;count= number;

while (count >=0) {

answer=answer* count;

count--;

}

printf ("%d!=%d\n",

number,answer);

return 0;

}

number=4

answer=1

count=4

enter whileloop

answer=1*4=4

count=3

enter whileloopanswer=4*3=12

count=2

enter whileloop

answer=12*2=24

count=1

enter whileloop

answer=24*1=24

count=0

enter whileloop

answer=24*0=0


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FunctionsFunctions

int fac(int n); /* function declaration */

int x=7;

printf(fac(%d)=%d\n,x, fac(x)); /* call function fac()*/

int fac(int n) /* function definition */

{

int i;

int result=1;for (i=1; i


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FunctionsFunctions

int pow(int a, int b); /* function declaration */

int a=3;

Int b=4;

printf(%d ^ %d =%d\n,a,b,pow(a,b)); /* call function fac()*/

int pow(int a, int b) /* function definition */

{

int result=1;

int i;for (i=1; i


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Pointers are variables that containPointers are variables that contain memorymemory addressesaddresses

as their values.as their values.

A variable nameA variable name directlydirectly references a value.references a value.

A pointerA pointer indirectlyindirectly references a value. Referencing areferences a value. Referencing avalue through a pointer is calledvalue through a pointer is calledindirectionindirection..

A pointer variable must be declaredbefore it can beA pointer variable must be declaredbefore it can be

used.used.

POINTERSPOINTERS

POINTERSPOINTERS


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POINTERSPOINTERS

A pointer is an address of a storage locationA pointer is an address of a storage location

By convention, zero represents the "null"By convention, zero represents the "null"pointerpointer

A pointer is a number, and must itself beA pointer is a number, and must itself be

storedstored The size of a pointer depends on the amountThe size of a pointer depends on the amount

of memory to be addressedof memory to be addressed

A 16A 16--bit pointer can address 64K locationsbit pointer can address 64K locations

A 32A 32--bit pointer can address 4 trillionbit pointer can address 4 trillionlocationslocations

POINTERSPOINTERS


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POINTERSPOINTERS Examples of pointer declarations:Examples of pointer declarations:

intint *a*a;;

floatfloat*b*b;;

charchar *c*c;;

TheThe asteriskasterisk, when used as above in the declaration,, when used as above in the declaration,tells the compiler that the variable is to be a pointer,tells the compiler that the variable is to be a pointer,and the type of data that the pointer points to, butand the type of data that the pointer points to, butNOTNOT the name of the variable pointed to.the name of the variable pointed to.

PointersPointers


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PointersPointers

Each variable in a program occupies a part ofEach variable in a program occupies a part ofthe computers memory, for example anthe computers memory, for example aninteger variable occupies 2 bytes of memoryinteger variable occupies 2 bytes of memory

The location of the piece of memory used toThe location of the piece of memory used to

store a variable is called the address of thatstore a variable is called the address of thatvariablevariable

An address is some kind of number similar toAn address is some kind of number similar to

house numbers in a street that is used tohouse numbers in a street that is used tolocate the information stored in thatlocate the information stored in thatparticular variableparticular variable


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PointersPointers

Pointers are used to:Pointers are used to: Access array elementsAccess array elements

Passing arguments to functions when thePassing arguments to functions when the

function needs to modify the original argumentfunction needs to modify the original argument Passing arrays and strings to functionsPassing arrays and strings to functions

Obtaining memory from the systemObtaining memory from the system

Creating data structures such as linked listsCreating data structures such as linked lists


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Use of & and *Use of & and * When is & used?When is & used?

When is * used?When is * used?

&& ---- "address operator" which gives or produces the"address operator" which gives or produces thememory address of a data variablememory address of a data variable

** ---- "dereferencing operator" which provides the"dereferencing operator" which provides thecontents in the memory location specified by a pointercontents in the memory location specified by a pointer

/*Program to swap the values of two variables in memory/*Program to swap the values of two variables in memory


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#include#includevoid exchange(int*,int*)void exchange(int*,int*)int main()int main(){{ int a,b;int a,b;

pf(Enter values of a and b); sf(%d%d&a,&b);pf(Enter values of a and b); sf(%d%d&a,&b);pf(Before exchange a=%d b=%d,a,b);pf(Before exchange a=%d b=%d,a,b);

exchange(&a,&b); pf(After exchange a=%d b=%d,a,b);exchange(&a,&b); pf(After exchange a=%d b=%d,a,b);return 0;return 0;

}}void exchange(int *aptr, int *bptr)void exchange(int *aptr, int *bptr){{ int temp;int temp;

temp=*aptr;temp=*aptr;

*aptr=*bptr;*aptr=*bptr;*bptr=temp;*bptr=temp;

}}

POINTER VARIABLESPOINTER VARIABLES


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POINTER VARIABLESPOINTER VARIABLES A pointer variable is a variable that holds address valuesA pointer variable is a variable that holds address values

Each data type has its own pointer variable, pointer toEach data type has its own pointer variable, pointer tointint, pointer to, pointer to doubledouble, pointer to, pointer to charchar, ,

C uses theC uses the addressaddress--ofof operator& to get the address ofoperator& to get the address ofan variablean variable

C uses theC uses the indirectionindirection oror contentscontents--ofof operator* tooperator* toaccess the value of the variable pointedbyaccess the value of the variable pointedby

int i=17;int i=17;

int* ptr; /* defines a pointer variable for integer variables */int* ptr; /* defines a pointer variable for integer variables */

ptr= &i; /* assign the address of i to pointer */ptr= &i; /* assign the address of i to pointer */printf(the value of i can be printed as %d or %dprintf(the value of i can be printed as %d or %d\\n, *ptr, i);n, *ptr, i);

printf(the address of i is %dprintf(the address of i is %d\\n, ptr);n, ptr);


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Pointer VariablesPointer Variables

0x1054int i;

17int *ptr;

ptr=&i;

printf(value of i = %d\n,*ptr);


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Pointer VariablesPointer Variables

int v; // defines variable v of type intint v; // defines variable v of type int

int w; // defines variable w of type intint w; // defines variable w of type int

int *p; // defines variable p of type pointer to intint *p; // defines variable p of type pointer to int

p=&v; // assigns address of v to pointer pp=&v; // assigns address of v to pointer p

v=3; // assigns value 3 to vv=3; // assigns value 3 to v

*p=7; // assigns value 7 to v*p=7; // assigns value 7 to v

p=&w; // assigns address of w to pointer pp=&w; // assigns address of w to pointer p

*p=12; // assigns value 12 to w*p=12; // assigns value 12 to w

Using the indirection operator *p to access theUsing the indirection operator *p to access thecontents of a variable is calledcontents of a variable is called indirect addressingindirect addressing

oror dereferencingdereferencing the pointerthe pointer


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PassPassbyby--ValueValue

when passing arguments by value, the function createsnew local variables to hold the values of the variableargument

the value of the original variable are not changed

void f(int val) /* the parameter val holds a local copy of thevariable argument */

{

val++;

}

int x=4;

f(x); /* call function f passing x by value */

printf(x=%d\n,x); /* x still has the value 4 */

Pointers as Function ArgumentsPointers as Function Arguments


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Pointers as Function ArgumentsPointers as Function Arguments

C offers two different ways to pass arguments to aC offers two different ways to pass arguments to a

functionfunction by value : void f(int x);by value : void f(int x);

by reference : void f(int* x);by reference : void f(int* x);

In passIn pass--byby--value the function obtains only a localvalue the function obtains only a local

copy of the variable, so that changes to the localcopy of the variable, so that changes to the localvariable have no impact on the argument with whichvariable have no impact on the argument with whichthe function was invokedthe function was invoked

In passIn pass--byby--reference the function manipulates thereference the function manipulates theoriginal variable rather than merely its copyoriginal variable rather than merely its copy

PassPass--byby--ReferenceReference


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yy

void swap( double* ptr1, double* ptr2)void swap( double* ptr1, double* ptr2){{double tmp=*ptr1;double tmp=*ptr1;*ptr1=*ptr2; /* de*ptr1=*ptr2; /* de--referencing pointer */referencing pointer */*ptr2=tmp;*ptr2=tmp;

}}

int main()int main(){{double a=3.0;double a=3.0;double b=5.0double b=5.0swap(&a, &b); /* call by reference using the addresses of a and b */swap(&a, &b); /* call by reference using the addresses of a and b */printf(a=%lf, b=%lfprintf(a=%lf, b=%lf\\n,a,b);n,a,b);

}}

*/Factorial of a given number using pointers*/*/Factorial of a given number using pointers*/


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g g pg g p

main()main()

{{ int n,factorial;int n,factorial;printf(enter a number);printf(enter a number);scanf(%d,&n);scanf(%d,&n);factcompute(n,&factorial);factcompute(n,&factorial);printf(the factorial of %d,n,factorial);printf(the factorial of %d,n,factorial);

}}factcompute(a,b)factcompute(a,b)int a,*b;int a,*b;{{

int m; *b=1;int m; *b=1;for(m=1;m


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ArraysArrays

The idea of an array is to group similarThe idea of an array is to group similarobjects into units.objects into units.

Arrays are structures that group itemsArrays are structures that group items

of the same data type.of the same data type.

The elements of an array are accessedThe elements of an array are accessedby an index number that allows randomby an index number that allows random

access.access.


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ArraysArrays

int poweroftwo[10]; /*array definition */int poweroftwo[10]; /*array definition */

int poweroftwo[0]=1; /* first element hasint poweroftwo[0]=1; /* first element has

index number 0 */index number 0 */

int i;int i;

for (i=1;i


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ArraysArrays

double avg(int sz, double array[]); /* function definition*/double avg(int sz, double array[]); /* function definition*/

double x[5]={1.2, 2.5, 1.7, 4.2, 3.9} /* initialize array */double x[5]={1.2, 2.5, 1.7, 4.2, 3.9} /* initialize array */

printf(average is %lfprintf(average is %lf\\n,avg(5,x));n,avg(5,x));

double avg(int sz, double array[])double avg(int sz, double array[]){{

int i;int i;

double sum;double sum;

for (i=0; i


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MultiMulti--Dimensional ArraysDimensional Arrays

#define ROWS 5#define ROWS 5#define COLS 6#define COLS 6

double matrix[ROWS][COLS];double matrix[ROWS][COLS];

double a[COLS];double a[COLS];

double b[ROWS];double b[ROWS];

int i,j;int i,j;

for(i=0;i


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an array */an array */ #include#include

#define MAXSIZE 100#define MAXSIZE 100main()main(){{

int n,I,max=0,elements[MAXSIZE];int n,I,max=0,elements[MAXSIZE];printf(enter the no of elements);printf(enter the no of elements);scanf(%d,&n);scanf(%d,&n);

for(i=0, i


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Arrays in PointersArrays in Pointers Array indexing is syntactic sugar for pointersArray indexing is syntactic sugar for pointers

a[i]a[i] is treated asis treated as *(a+i)*(a+i) To zero out an array:To zero out an array:

for (i = 0; i < size; i++)a[i] = 0;for (i = 0; i < size; i++)a[i] = 0;

for (i = 0; i < size; i++)*(a+i) = 0;for (i = 0; i < size; i++)*(a+i) = 0;

for (p = a; P < a+size; p++)*p = 0;for (p = a; P < a+size; p++)*p = 0;

BecauseBecause a[i]a[i] meansmeans *(a+i),i[a]*(a+i),i[a]is equally legal!is equally legal!

Pointers and ArraysPointers and Arrays


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Pointers and ArraysPointers and Arrays There is a close association between pointers and arraysThere is a close association between pointers and arrays

Arrays can be accessed using pointersArrays can be accessed using pointers The name of an array is also a constant pointer to the dataThe name of an array is also a constant pointer to the data

type of the elements stored in the arraytype of the elements stored in the array

int array[5] = { 23, 5, 12, 34, 17 }; /* array of 5 ints */int array[5] = { 23, 5, 12, 34, 17 }; /* array of 5 ints */

for (int i=0; i


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Arrays and StringsArrays and Strings In C there is no particular type for strings.In C there is no particular type for strings.

Instead strings are stored in arrays of typeInstead strings are stored in arrays of typecharacter.character.

#include #include

char lastname[256]=Hansen;char lastname[256]=Hansen;char firstname[256]=Ole;char firstname[256]=Ole;

char fullname[512];char fullname[512];

strcpy(fullname,firstname);strcpy(fullname,firstname);

strcat(fullname, );strcat(fullname, );strcat(fullname,lastname);strcat(fullname,lastname);

printf(full name is %sprintf(full name is %s\\n,fullname);n,fullname);

StructuresStructures


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StructuresStructures A structure is a collection of simple variables, that can be ofA structure is a collection of simple variables, that can be of

different type.different type.

The data items in a structure are called members of the structure.The data items in a structure are called members of the structure.

struct complex /* structure declaration */struct complex /* structure declaration */

{{

double re; /* members of the structure */double re; /* members of the structure */

double im;double im;

};};

complex mult(struct complex a, struct complex b);complex mult(struct complex a, struct complex b);

struct complex a,b,c; /* variable declaration of type complex */struct complex a,b,c; /* variable declaration of type complex */

a.re=2.0; /* accessing members of struct complex */a.re=2.0; /* accessing members of struct complex */

a.im=1.5;a.im=1.5;

b.re=2.3;b.re=2.3;

b.im=b.im=--1.8;1.8;

c=mult(a,b);c=mult(a,b);

C StructuresC Structures


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C StructuresC Structures Collection of related variables under one nameCollection of related variables under one name

Derived data typesDerived data types Variables declared within the braces of the structureVariables declared within the braces of the structure

definition are the members of the structuredefinition are the members of the structure Members of the same structure type must haveMembers of the same structure type must have

unique namesunique names

Two different structure types can contain members ofTwo different structure types can contain members ofthe same name without conflictthe same name without conflict

struct card {struct card {int face;int face;

char suit[20];char suit[20];};};

struct card aCard, deck[52], *cardPtr;struct card aCard, deck[52], *cardPtr;

StructuresStructures


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StructuresStructures Structures are collections of variables ofStructures are collections of variables of

different types, as in the followingdifferent types, as in the followingexample.example.

struct abc

{

int a;

long b;

char c;}

MyStruct;

Structure

Definition

variable

declaration

StructureType

Name

d id i


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C Structures and FunctionsC Structures and Functions

struct point makepoint(struct point pt, int x, int y) {struct point makepoint(struct point pt, int x, int y) {

pt.x = x;pt.x = x;

pt.y = y;pt.y = y;

return pt;return pt;

}}

int main() {int main() {

struct point pt;struct point pt;

pt = makepoint (pt, 5, 6);pt = makepoint (pt, 5, 6);printf(pt.x = %d pt.y = %dprintf(pt.x = %d pt.y = %d\\n, pt.x, pt.y);n, pt.x, pt.y);

}}

C S d iC S d i


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C Structures and FunctionsC Structures and Functions

void makepoint(struct point *pt, int x, int y) {void makepoint(struct point *pt, int x, int y) {

ptpt-->x = x;>x = x;

ptpt-->y = y;>y = y;

}}

int main() {int main() {

struct point pt;struct point pt;

makepoint (&pt, 5, 6);makepoint (&pt, 5, 6);

printf(pt.x = %d pt.y = %dprintf(pt.x = %d pt.y = %d\\n, pt.x, pt.y);n, pt.x, pt.y);

}}

For very large structures, pass the pointer to it!For very large structures, pass the pointer to it!


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/*Program to display the month names of both dates*//*Program to display the month names of both dates*/ Struct mydateStruct mydate

{{ int yyyy;int yyyy;int mmdd;int mmdd;};};main()main(){{ struct mydate date1,date2;struct mydate date1,date2;

int month1,month2;int month1,month2;

char *months[]={ ,jan,feb,mar,.dec};char *months[]={ ,jan,feb,mar,.dec};pf(enter first date(mmdd)); sf(%d,&date1.mmdd);pf(enter first date(mmdd)); sf(%d,&date1.mmdd);

pf(enter second date(mmdd)); sf(%d,&date2.mmdd);pf(enter second date(mmdd)); sf(%d,&date2.mmdd);month1month1--date1.mmdd/100;month2=date2.mmdd/100;//take month alonedate1.mmdd/100;month2=date2.mmdd/100;//take month alonepf(firstt month is %s,months[month1];pf(firstt month is %s,months[month1];

pf(second month is %s,months[month2]);pf(second month is %s,months[month2]);}}


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/*Program to illustrate the use of structure pointer/*Program to illustrate the use of structure pointer

Struct currencyStruct currency{{ int rupees;int rupees;

int paise;int paise;};};main()main(){{ struct currency mycurr={123,25};struct currency mycurr={123,25};

showit(&mycurr);showit(&mycurr);}}showit(struct currency *myptr)showit(struct currency *myptr)

{{ pf(rupees %d,%d,myptrpf(rupees %d,%d,myptrrupees,myptrrupees,myptrpaise);paise);}}

U iU i


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UnionsUnions

Unions look similar to structures. They have identicalUnions look similar to structures. They have identicaldeclaration syntax and member access, but they serve adeclaration syntax and member access, but they serve avery different purpose.very different purpose.

union Utype {union Utype {

int ival;int ival;float fval;float fval;

char *sval;char *sval;

};};

u

nion Utype x, y, z;u

nion Utype x, y, z;

Accessing members of a union is via Accessing members of a union is via .. member operator member operatoror, for pointers to unions, theor, for pointers to unions, the -->> operator.operator.

U iU i


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UnionsUnions

A union holds the value of oneA union holds the value of one--variable at a time.variable at a time.

The compiler allocates storage for theThe compiler allocates storage for the biggestbiggestmember of the union.member of the union.

The type retrieved from the union must be the typeThe type retrieved from the union must be the typemost recently stored. Otherwise, the result ismost recently stored. Otherwise, the result isimplementation dependent.implementation dependent.

union Utype x;union Utype x;

x.fval = 56.4;x.fval = 56.4; /* x holds type float. *//* x holds type float. */printf("%fprintf("%f\\n", x.fval); /* OK. */n", x.fval); /* OK. */

printf("%dprintf("%d\\n", x.ival); /* Implementationn", x.ival); /* Implementation

dependent. */dependent. */

U iU i


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UnionsUnions

Unions are used to store one of a set of different types.Unions are used to store one of a set of different types.

Commonly used to implement a variant array. (This isCommonly used to implement a variant array. (This isa form of generic programming.)a form of generic programming.)

There are other uses also, but they are quite advancedThere are other uses also, but they are quite advanced(e.g., concern the alignment properties of unions).(e.g., concern the alignment properties of unions).

/* Write a c/* Write a c--program for student marksprogram for student marks


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p gp gusing an array of structures */using an array of structures */

struct marksstruct marks{{ int sub1; int sub2;int sub1; int sub2;

int sub3; int total;int sub3; int total; };};

main()main()

{{ int i;int i;

static struct marks student[3]={static struct marks student[3]={{56,45,65},{56,45,65},

{59,55,75},45,65,75}};{59,55,75},45,65,75}};

static struct marks total;static struct marks total;

for(i=0;i


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printf(STUDENTprintf(STUDENT TOTAL);TOTAL);for(i=0;i


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File Input In CFile Input In C

C program

FILE

The C type, FILE allows for a consistent approach to input

regardless of the actual physical device

Default: stdin

Fil O t t I CFil O t t I C


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File Output In CFile Output In C

C program

FILE

Similar to file input, the C type FILE allows for a consistent

approach to output regardless of the actual physical device

stream

Default: stdout

D l i g FILE V i blD l i g FILE V i bl


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Declaring a FILE VariableDeclaring a FILE Variable

Format:Format: FILE *;

Example:Example: FILE *fp;FILE *fp;

Be sure to include the followingBe sure to include the following

preprocessors:preprocessors: #include #include #include #include

Opening FilesOpening Files


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Opening FilesOpening Files

Format:Format:

FILE * fopen (const char * filename, const char *FILE * fopen (const char * filename, const char *mode);mode);

Example:Example:

fp = fopen (data, r);fp = fopen (data, r);

fp = fopen (/home/profs/tamj/data, r);fp = fopen (/home/profs/tamj/data, r);

ErrorconditionsErrorconditions File does not exist.File does not exist.

Insufficient permissions to open the file.Insufficient permissions to open the file.

Opening Files (2)Opening Files (2)


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p g ( )p g ( ) FilenameFilename

Must reside in the same directory as C programMust reside in the same directory as C programbeing runbeing run

Alternatively you can include the path to the fileAlternatively you can include the path to the file

Some File open modesSome File open modes

ModeMode Effect Effect

rr Open text file for readingOpen text file for reading

ww Open text file for writingOpen text file for writing

aa Open text file for writing, start writing atOpen text file for writing, start writing atthe endthe end

r+r+ Open file for reading and writingOpen file for reading and writing

w+w+ Open file for writing and readingOpen file for writing and reading

Closing FilesClosing Files


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Closing FilesClosing Files Disassociates the file with the physical deviceDisassociates the file with the physical device

Remaining contents of the stream a flushedRemaining contents of the stream a flushed

Format:Format:

int fclose (FILE * fp);int fclose (FILE * fp);

Example:Example:

fclose(fp);fclose(fp);

Writing ToA File fprintfWriting ToA File fprintf


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Format:Format:

fprintf (FILE *fp, const char *control_string,fprintf (FILE *fp, const char *control_string,arguments);arguments);

Example:Example:

char arr[8] = hiya;char arr[8] = hiya;

fprintf(fp, %s, arr);fprintf(fp, %s, arr);

Similar to printf except you can also write to a file otherSimilar to printf except you can also write to a file other

than the screen (standard out).than the screen (standard out).

Reading From A File fscanfReading From A File fscanf


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Format:Format:

fscanf (FILE *fp, ,fscanf (FILE *fp, ,addresses);addresses);

Example:Example: char arr[8];char arr[8];

fscanf (fp, %s, chunk);fscanf (fp, %s, chunk);

Similar to scanf except you can also read from aSimilar to scanf except you can also read from afile other than the keyboard (standard in)file other than the keyboard (standard in)

Reading From A File fgetsReading From A File fgets


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Reading From A File fgetsReading From A File fgets

Format:Format:

fgets(char *line, int n, FILE *fp);fgets(char *line, int n, FILE *fp);

Example:Example:

fgets(chunk, 80, fp);fgets(chunk, 80, fp);

File I/O: First ExampleFile I/O: First Example


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The full example can be found in CThe full example can be found in C::

#include #include #include #include int const LENGTH = 80;int const LENGTH = 80;main ()main (){{

FILE *fp_in, *fp_out ;FILE *fp_in, *fp_out ; char arr[LENGTH];char arr[LENGTH]; char fn_in [LENGTH];char fn_in [LENGTH]; char fn_out [LENGTH];char fn_out [LENGTH];

printf("Enter name of input file: ");printf("Enter name of input file: "); scanf("%s", fn_in);scanf("%s", fn_in); printf("Enter name of output file: ");printf("Enter name of output file: "); scanf("%s", fn_out);scanf("%s", fn_out);

File I/O: First Example (2)File I/O: First Example (2)


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fp_in = fopen(fn_in, "r");fp_in = fopen(fn_in, "r"); fp_out = fopen(fn_out, "w");fp_out = fopen(fn_out, "w");

if (!fp_in)if (!fp_in) {{ printf("Can't open input fileprintf("Can't open input file\\n");n"); return(return(--1);1); }}

if (!fp_out)if (!fp_out) {{ printf("Can't open output fileprintf("Can't open output file\\n");n"); return(return(--1);1); }}



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while (feof(fp_in) == 0)while (feof(fp_in) == 0)

{{

// Using fscanf it stops scanning at whitespace// Using fscanf it stops scanning at whitespace

fscanf(fp_in, "%s", arr);fscanf(fp_in, "%s", arr);

fprintf(fp_out, "%sfprintf(fp_out, "%s--", arr);", arr);

}}

return(0);return(0);

}}

File I/O: Second ExampleFile I/O: Second Example


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This example is identical to the first example except for theThis example is identical to the first example except for theloop:loop:

while (feof(fp_in) == 0)while (feof(fp_in) == 0)

{{

// Grabs whole line up 79 characters or the end// Grabs whole line up 79 characters or the end--ofof--filefile(whichever comes first)(whichever comes first)

fgets (arr, 80, fp_in);fgets (arr, 80, fp_in);

// Writes out to output file as// Writes out to output file as--is.is.

fprintf (fp_out, "%s", arr);fprintf (fp_out, "%s", arr);

}}

File I/O: Third ExampleFile I/O: Third Example


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#include #include

#include #include

int const LENGTH = 80;int const LENGTH = 80;

main ()main ()

{{ FILE *fp_in;FILE *fp_in;

char arr[LENGTH];char arr[LENGTH];

char fn_in [LENGTH];char fn_in [LENGTH];

printf("Enter name of input file: ");printf("Enter name of input file: ");

scanf("%s", fn_in);scanf("%s", fn_in);

File I/O: Third Example (2)File I/O: Third Example (2)


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fp_in = fopen(fn_in, "r");fp_in = fopen(fn_in, "r"); if (!fp_in)if (!fp_in) {{ printf("Can't open input fileprintf("Can't open input file\\n");n"); return(return(--1);1); }}

while (feof(fp_in) == 0)while (feof(fp_in) == 0) {{ // Grabs whole line up 79 characters or the end// Grabs whole line up 79 characters or the end--ofof--filefile fgets(arr, 80, fp_in);fgets(arr, 80, fp_in);

// Writes out to output file as// Writes out to output file as--is. Output file is the screenis. Output file is the screen fprintf(fprintf(stdoutstdout, "%s", arr);, "%s", arr); }} return(0);return(0); }}

/* Write a program to detect error while opening a file that/* Write a program to detect error while opening a file thatdoes not exist.*/does not exist.*/


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#include#includemain()main()

{{ char *filename;char *filename;FILE *fp1,*fp2;FILE *fp1,*fp2;int i, number;int i, number;fp1=fopen(TEST,w);fp1=fopen(TEST,w);for(i=10;i


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elseelse

for(i=1;i


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It is the process of calling of a function by itself. The functionwhich calls itself is known as recursive function.

EXAMPLE: TO CALCUALTE FACTORIAL OF A NUMBER

int factorial(int);void main(){

int num,f;printf(enter number whose factorial is to be

calculated);scanf(%d,&num);f=factorial(num);

printf(%d,f);}

Contd

int factorial(int x)


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int factorial(int x){

if(x==1)return 1;elsereturn x*factorial(x-1);}


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THANX

13878_C-Language (All Concepts)

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