Using Pointers (continues)

int  int1     = 1036;   /* some data to point to  */

int  int2     = 8;

int *int_ptr1 = &int1;  /* get addresses of data  */

int *int_ptr2 = &int2;

int_ptr1 = *int_ptr2;

int_ptr1 = int_ptr2;

Changes happen:

1.Type check warning:  *int_ptr2 is not an int *

2.Changes int_ptr1 – doesn’t change int1

Using Pointers (cont.)

int  int1     = 1036;   /* some data to point to  */

int  int2     = 8;

int *int_ptr1 = &int1;  /* get addresses of data  */

int *int_ptr2 = &int2;

*int_ptr1 = int_ptr2;

*int_ptr1 = int2;

int1 becomes 8

Type check warning:  int_ptr2 is not an int

Using Pointers

int  i1;

int  i2;

int *ptr1;

int *ptr2;

i1 = 1;

i2 = 2;

ptr1 = &i1;//ptr1 points to address 0x1000

ptr2 = ptr1;//ptr2 takes address of ptr1 and so ptr2 points to   address 0x1000

*ptr1 = 3;//value of i1(to which ptr1 pointed becomes 3

i2 = *ptr2;//as i1=3,*ptr2=*ptr1=3,so i2 becomes 3

Pointer Operations in C

Creation

& variable  Returns variable’s memory address

Dereference

* pointer  Returns contents stored at address

Indirect assignment

* pointer = val  Stores value at address

Assignment

pointer = ptr  Stores pointer in another variable

eg. 

      if a variable  is a=24 and it is stored at memory address 2000.Consider we want to point a pointer named p at that variable,do following things.

int *p,a=24,b,c;//initializing the pointers

*p=&a;//stores 2000 address to the pointer's address

b=*p;//outputs as '24' as it returns content of pointer

*p=55;//directly stores the value at address 2000

c=p;//stores the pointer

  

Pointers

Special case of bounded-size natural numbers

Maximum memory limited by processor word-size

232 bytes = 4GB, 264 bytes = 16 exabytes

A pointer is just another kind of value

A basic type in C

 

eg. int *ptr

The variable “ptr” is a pointer to an “int”,the datatype.

Memory Addresses

1.Storage cells are typically viewed as being byte-sized
 

Usually the smallest addressable unit of memory
 

•Few machines can directly access bits individually
 

Such addresses are sometimes called byte-addresses
 

2.Memory is often accessed as words

 

Usually a word is the largest unit of memory access by a single machine instruction
 

CLEAR’s word size is 8 bytes (= sizeof(long))

 

 A word-address is simply the byte-address of the word’s first byte

Expressions

•Constant
–25+5

•Integral
–M*x assume M and x are both integer

•Float
–Sum/9

•Pointer
–Ptr++

•Relational
–X<=y

•Logical

–A>b && b<c

Data types and operators

•Built-in type
–Integer,float,charetc.
•Derived data types
–Array,pointeretc.
•User defined data type
–Structure, union, class, enumeration.
•Operators
–Arithmetic
–Assignment
–Increment/decrement
–Unary
–Relational
–Ternary
–Logical
–bitwise

Basic Commands

C statement

Printf(“%d”,a); //to print variable "a"

Equivalent C++ statement

Cout<<a;

C statement

Scanf(“%f”,&average); //to get the value and store in vaiable "average"

Equivalent C++ statement

Cin>>average;

C statement
Printf(“total is %d this ”,sum);//to print the variable 'sum'

Equivalent C++ statement

Cout<<“totalis“<<sum<<“ this”;

C statement
Scanf(“%d %f”,&a,&x);//to get and store the value of vaeiables 'a' and 'x'

Equivalent C++ statement

Cin>>a>>x;

GTU syllabus for OOCP

Dear friends,if you are a GTU 4th sem student and OOCP is one of your subject,here is a link of your subject syllabus.Click here to download it.

Introduction of C++

C++ was developed by Bjarne Stroustrup of AT&T to add objectoriented
constructs to the C language. Because object-oriented
methodology was relatively new at the time, and all existing
implementations of object-oriented languages were rather slow and
inefficient (most were interpreters), one goal of C++ was to maintain
the efficiency of C.