Review of c Concept

8/9/2019 Review of c Concept

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1Prof. Shylaja S S, Head, ISE, PESIT


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DATA TYPES:

Definition : Thetypeof thedatathata variable can store in the memory can bedefined using data types.

Significance :1. Memory allocation is done according to the

data type

2. Permissible operations3. Range of data



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DATA TYPES (CONTD.) :

DATA TYPES

PRIMARY DERIVEDUSER

DEFINEDEMPTYPRIMARY DERIVED



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Primary type :int , float , double, char

Derived type : (derived from primary)

arrays , pointers

User-defined :

structures , unions

Empty :

void 4Prof. Shylaja S S, Head, ISE, PESIT


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QUALIFIERS

SIGN

SIZE

SIGN QUALIFIERS : Signed , unsigned (for primary

d a t a t y p e s )

SIZE QUALIFIERS :Short , long



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PRACTICE PROGRAM : To add 2 numbers

#include

void main( )

{

int a , b , sum ;

printf(Enter 2 numbers \n );

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

sum= a +b ;

printf(Sum = %d , sum );

}

CASE1 :

If input is 123 , 24

Output : 147

CASE2 :If input is

123567+24111

Program does not

work as input is out of therangefor

integer data type



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VARIABLES :

Definition : Identifier whosevaluecanbe changed during program execution

Remember :

1. Important to choose name of variable

appropriately.(useful in long programs)

2.Choose variable name as per the rulesdefined



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OPERATORS :TYPES

ARITHMETIC

ASSIGNMENT

Increment/Decrement

RELATIONAL

LOGICAL

CONDITIONAL

BITWISE

SPECIAL 8Prof. Shylaja S S, Head, ISE, PESIT


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OPERATORS (CONTD.):Arithmetic: + , - , / , * . %

Assignment : =,{+= , *= etc ->shorthand operators)}

Increment/Decrement : ++ , --

Relational : < , , >= , == , !=

Logical : ! , && , | |

Conditional : ?

Bitwise : ~ , > , & , ^ , |

Special operators : ,(comma) , sizeof , & (address

operator)



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OPERATORS (CONTD.):

IMPORTANT: PRECEDENCE AND

ASSOCIATIVITY

Simple examples to demonstrate the above :

if a=2 , b=5 , c=3 , m=8

1. a+b+c = 10

L to R associativity for same operatorThus, ((a+b)+c)= ((2+5)+3)= (7+3)= 10



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OPERATORS (CONTD.):2. a+b*c=17

Precedence of * operatorThus , (a+(b*c)) = (2+(5*3)) = (2+15) = 17

3 . d= a >b ? c > m? a : b : c

R to L associativity for conditional operator

Thus , d = (a>b?(c>m?a:b):c)= (2>5?(3>8?2:5):3)

= (2>5?5:3)

d = 3 11Prof. Shylaja S S, Head, ISE, PESIT


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OPERATORS (CONTD.):

WHAT IS THE OUTPUT ??????

i=5;

printf ( %d , %d , %d , %d , i++ , i , i++ , ++i );

7 , 7 , 6 , 6 OR 7 , 8 , 6 , 6

(R to L execution) (PRECEDENCE OF UNARY(++) OPERATOR )

NOTE : COMPILER DEPENDENT 12Prof. Shylaja S S, Head, ISE, PESIT


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Set of similar elements

Homogenous

Continuous memory

Derived data type

ARRAY :

KEY POINTS :-



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ARRAY (contd .):

TYPES

1-DIMENSIONAL 2-DIMENSIONAL

SYNTAX :

datatype arrayname[size];

Size should be a constant

For eg : int arr[10]; 14Prof. Shylaja S S, Head, ISE, PESIT


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STRUCTURES AND UNIONS :

SIMILARITY :1.User-defined

2.Collection of related items

3.Heterogenous in nature

DIFFERENCES :1.Memory allocation for variable

2.Memory access15Prof. Shylaja S S, Head, ISE, PESIT


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INPUT AND OUTPUT :

DATA FLOW

INPUT OPERATION OUTPUT OPERATION

(Data flows from

the externaldevice into the

program)

(Data flows from

the program tothe external

device)

(Data flows from

the externaldevice into the

program)

(Data flows from

the program tothe external

device)16Prof. Shylaja S S, Head, ISE, PESIT


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INPUT AND OUTPUT (contd.):

Formatted functions

scanf

printf

(use format specifiers)

(Input function)

(Output function)

UNFORMATTED FUNCTIONS :

gets

puts17Prof. Shylaja S S, Head, ISE, PESIT


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IMPORTANT CONCEPT :

Width specification ( %wd)Mainly used for beautification of output

Example : int i=284;

printf(%d , %2d , %3d,i);

Output : 284,284,284Excercise :

See the difference in the output when youexecute the following 2 codes :


for (i=1; i


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WILL THE PROGRAM WORK ?????

void main( )

{

char *p;

gets ( p ) ;

puts ( p );

}



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FUNCTIONS :

ADVANTAGES :

1.Debugging

2.Reusability

3.Readability

4.Memory

DISADVANTAGES :

Execution time ismore

A subprogram/module which performs a

specific task



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STORAGE CLASSES :

Talk about the SCOPE (who can access) & LIFETIME (how long it is alive) of a VARIABLE

TYPES

AUTO STATIC EXTERN REGISTER



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STORAGE CLASSES (Contd.):

KEY POINTS : Auto local and static local have a function scope

Register mainly used for faster access of the

variable Extern declaration more important across files

Auto global variables can be used in more than

one file using extern declaration

Static global variables can be accessed only by

functions in the file



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STORAGE CLASSES (Contd.):Programs to understand key concepts of storage classes :

1.

void fn (int n)

{ n++; }

void main()

{ autoint i =5;

fn(i);

printf(%d\n,i);fn(i);

printf(%d,i);

}

Output :

5

5



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STORAGE CLASSES (Contd.):2.

void fn (int n)

{ n++; }

void main()

{ staticint i =5;

fn(i);

printf(%d\n,i);

fn(i);

printf(%d,i);

}

Output :

6

7



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STORAGE CLASSES (Contd.):

Program to illustrate importance of extern declaration

int i; //global

void main( )

{

printf( %d , i ) ;}

voidf1( )

{ i++; }

voidf2( )

{ i++; }

OUTPUT: 0

void main( )

{

printf( %d , i ) ;

}

int i; //global only to f1,f2

voidf1( )

{ i++; }

voidf2( )

{ i++; }

Thus,undefined symbol i

(error)

void main( ){

extern int i;

//declaration

printf( %d , i) ;

}

int i; //definition

voidf1( )

{ i++; } voidf2( )

{ i++; }



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POINTERS : A pointer variable stores address of

another variable

int i =5;

int *p;

p=&i;

printf(%d\n,i);

printf(%d\n,*p);

*p =8;

5

i

1000

1000

p

2000

5

5

i8 1000 26Prof. Shylaja S S, Head, ISE, PESIT


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POINTERS (contd.) :Program to illustrate importance of pointers :

To swap contents of two variables using functions

Method 1 : GLOBAL VARIABLES

int a=2,b=3;

void swap( );

void main( )

{ swap( );

printf(After swapping :\n a=%d , b=%d,a , b);

}

voidswap() { int t;

t=a ; a =b ; b = t ; }

OUTPUT :

After swapping :a=3 , b =2



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POINTERS (contd.) :METHOD2: PASSBYVALUE

void swap (int , int );void main( )

{ int a=2,b=3;

swap(a,b);

printf (After swapping :\n a=%d , b=%d,a , b);

}

void swap (int a , int b)

{

int t;

t=a ;a =b ;

b = t ;

}

Output :

After swapping:

a=2 , b =3



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POINTERS (contd.) :METHOD 3 : PASS BY REFERENCE

voidswap(int *, int * );void main( )

{ int a=2,b=3;

swap(&a,&b);

printf (After swapping :\n a=%d , b=%d,a , b);

}

voidswap(int *i , int *j)

{

int t;

t=*i ;*i =*j ;

*j =t;

}

Output :

After swapping:

a=3 , b =2



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POINTERS (contd.) :

Why do we havepointers to

int , float etc ?????

1. To retreive / access

value

2. Pointer arithmetic

FOREG:

float *p;

i=*p;

// FETCH4 BYTESOFDATAANDASSIGNTOi



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POINTERS (contd.) :ARRAYS AND POINTERS : Arrays are constant pointers

Example program:

void main( ){

int a[3] = {5 , 6 , 7 } ;

f1 ( a , 3 ) ;

// a++ ; (array constant , thus , statement is incorrect)

}

void f1 (int *p , int n )

{ printf( %d\n,*p) ;

p++;

printf( %d\n,*p) ;

}

OUTPUT :

56



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POINTERS (contd.) :PRACTICE PROGRAM : To read one students marks and add a

grace of 5 marks using pass by reference

void main( )

{

float m;

scanf( %d ,&m);grace(&m);

printf( %d ,m);

}void grace (float *p)

{ *p = *p + 5 ; }

Input: 85

Output :

90

EXCERCISE :

REPEAT THE SAMEPROCEDURE FOR

MANY STUDENTS



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