Cpp tokens (2)

Classified e-Material ©Copyrights Charotar Institute of Technology, Changa 1
Department of Information Technology
Tokens, Expressions and
Control Structure
CE 142: Object Oriented
Programming with C++
Kamlesh Makvana

Course Outline
Sr
No.
Title of the unit
1 Tokens
2 Type Compatibility
3 Dynamic Initialization
4 Reference Variable
5 Operators in C++
6 Scope Resolution Operator
7 Expression and Control Structure

C++ Timeline

Tokens
 Tokens
 The Smallest Individual units in a program
 Types of Tokens
 Keywords
 Identifiers
 Constants
 String
 Operators

Keywords
 Implement specific C++ language
features
 They are explicitly reserved identifiers

Identifiers and Constants
 Name of Variable, function, array,
structure, Class etc.
 Rules to specify Identifiers
 Only alphabetic characters, digits,
underscores are permitted
 The name cannot start with a digit
 Uppercase and Lowercase letters are
distinct
 A declared keyword can not be used as a
variable name.

Identifiers and Constants
 The major difference between C and C++is the
limit on the length of variable.
 C-first 32 characters are recognized.
 C++- No Limit on length.
 Constants refers to fixed values.
 123 // Integer constant
 12.34 // floating point integer
 o37 // Octal integer
 0x2 // Hexadecimal integer
 “C++” // string constant
 ‘A’ // Character constant
 L ‘ab’ // Wide –character constant

Basic Data Types
 Built-in Type
 Integral Type
 int, char
 Floating Type
 float, double
 Void
 Derived Type
 array, function, pointer, reference
 User defined type
 Structure, union, enumeration, class

Void Data Type
 Where you are using void type?
 To specify return type of function.
 void function1()
 To represent empty argument list.
 int function2(Void)
 Declaration of Generic pointers.
 void *p
 But it can not be dereferenced!!!
 Assigning any pointer to void pointer is
allowed in both C and C++
 Can not Assign a void pointer to a non
void pointer without a type casting.

Enumerated Data Type
 Provides a way of attaching names to numbers.
 Automatically enumerates by assigning values
0,1,2, and so on.
 Syntax
 enum shape{circle, square, triangle};
 enum colour{red, blue, green, yellow}
 Difference in C and C++
 shape ellipse; //ellipse is of type shape
 couour background; //background is of type colour
 Anonymous enums
 enum{off,on};

Difference in C and C++

Anonymous enums

Storage Classes
 Automatic (Local Variable)
 Lifetime: Function Block, Visibility: Local, Initial value:
Garbage, Keyword: auto
 External (Global Variable)
 Lifetime: Entire Program , Visibility: Global, Initial
value: 0, Keyword: extern
 Static
 Lifetime: Entire Program , Visibility: Local, Initial
value: 0, Keyword: static
 Register
 Lifetime: Function Block , Visibility: Local, Initial value:
Garbage, Keyword: Register

Derived Data Type
 Array
 Group of Similar Data type.
 Char string[3]=“xyz”; // Valid in C
 Char string[3]=“xyz”; // Not Valid in C++
 Char string[4]=“xyz”; // OK;
 Pointer
 Example
 int *p,x;
 ip=&x;
 *ip=10;
 Constant Pointer and Pointer to constant

Constant Pointer and Pointer to
constant
 Constant pointer
 int a=10,b=20;
 int * const p1=&a;
 p1=&b; //Error
 Pointer to constant
 int a=10,b=20;
 int const *p1=&a;
 p1=&b; //Valid
 b++; //Valid
 (*p1)++; //Error

Symbolic Constant
 Two ways of creating symbolic constant
in C++
 Using the qualifier const
 const int size=10;
 const size=10;
 Defining a set of integer constant using
enum keyword.
 enum{x,y,z};=>const x=0;const y=1; const
z=2
 enum{x=100,y=50,z=200};

Type Compatibility
 C++ is very strict with regard to type
compatibility to C.
 short int, int, long int
 Unsigned char, char, signed char
 int is not compactible with char.
 Function overloading.

Variable
 Variable Declaration
 Declare a variable as needed
 Dynamic initialization
 Int m=10;
 Int a=m*10;
 Lambda Expression (C++ 11).

Reference Variable
 Alias for previously defined variable
 Syntax
 Data-type & reference-name=var-name
 Example:
 float total=100;
 float & sum=total;
 cout<<total<<sum;
 Total=total+10;
 cout<<total<<sum;
 Reference variable must initialize at time of
declaration.

Property of Reference
//Address of a & b are same

//Invalid Initialization of constant variable to non-constant reference

Some Other Properties
 Reference variable can never be void
 void &ar = a; // it is not valid
 Once a reference is created, it cannot
be later made to reference another
object
 References cannot be NULL (Expect
Constant Reference.).
 A reference must be initialized when
declared
 Can not be declared pointer to
reference.

Reference Variable
 Following statements are also allowed.
 int x; int *p=&x; int & m=*p;
 const int & n=50;
 Application of Reference variable
 Passing an argument to functions.
 Manipulation of object without copying object
arguments back and forth.
 Creating reference variable for user defined
data types.
 Creating Delegates in C++.

Exercise
30

Exercise
Error

Exercise

Exercise
Error

Exercise
Address of x

Exercise
Runtime Error.

Exercise
10

Exercise
30

Operators in C++
 :: Scope resolution operator
 ::* Pointer-to-member declaration
 ->* Pointer-to-member operator
 .* Pointer-to-member operator
 delete Memory release operator
 new Memory allocation operator
 setw Field width operators
 endl Line feed operator

:: Scope Resolution operator
 C++ is block structured language

:: Scope Resolution operator
 C++ is block structured language
 Two declaration of x refers to two
memory location containing different
values.
 In C global variable can not be accessed
from within the inner block
 :: operator solves this problem.
 Syntax:
 :: variable-name

Memory Management Operator
 Memory allocation in C:
 malloc()
 calloc()
 realloc()
 Deallocated using the free() function.
 Memory allocation in C++
 using the new operator.
 Deallocated using the delete operator.
 Syntax:
 Pointer-variable=new data-type

 Example:
 int *p=NULL;
 p=new int;
 int *p=new int;
 Int *p=new int(5);
 Allocating memory to array
 Syntax:
 Variable-name=new data-type[size];
 Example
 int *p = new int[10]

 What happens if sufficient memory is
not available?
 exception of type std::bad_alloc
 new operator returns a null pointer
 Example:
int *p
p=new int;
If(!p)
{
cout<<“Allocation failed n”;
}

 Advantages
 Automatically computes size of data
 It automatically returns the correct pointer
type
 Possible to initialize the object while
creating the memory space
 New and delete operator can be
overloaded!!!

Home Work
 Difference between delete and free.

Exercise
How to create a dynamic array of pointers (to integers)
of size 10 using new in C++?
Hint: We can create a non-dynamic array using
int *arr[10]
int **arr = new int *[10];

Exercise
Which of the following is true about new when
compared with malloc.
1)new is an operator, malloc is a function
2)new calls constructor, malloc doesn't
3)new returns appropriate pointer, malloc
returns void * and pointer needs to typecast to
appropriate type.
All

Exercise
No Effect
What happens when delete is used for a
NULL pointer?
int *ptr = NULL;
delete ptr;

Exercise

Manipulators
 Stream I/O Library Header Files
 iostream
 contains basic information required for all stream I/O
operations
 iomanip
 contains information useful for performing formatted
I/O with parameterized stream manipulators
 fstream
 contains information for performing file I/O operations
 strstream
 contains information for performing in-memory I/O
operations.

C++ Stream I/O -- Stream Manipulators
 C++ provides various stream manipulators
that perform formatting tasks.
 Stream manipulators are defined in
<iomanip>
 These manipulators provide capabilities for
 setting field widths,
 setting precision,
 setting and unsetting format flags,
 flushing streams,
 inserting a "newline" and flushing output
stream,
 skipping whitespace in input stream

setprecision (n)
 Select output precision, i.e., number of significant
digits to be printed.
 Example:
cout << setprecision (2) ; // two significant digits
setw (n)
 Specify the field width (Can be used on input or
output, but only applies to next insertion or
extraction).
 Example:
cout << setw (4) ; // field is four positions wide

Does setw set width of all variables specified
in cout?
No, Default alignment is
right

What about left alignment?

Does left alignment aligns all the
variables specified in cout?
alignment: yes
setw: No

Can more than one alignment is possible in
one cout cascading statement?
Yes

cout ignores 0 after decimal places

Default no. of digits in float is 6.

setprecision: specifies digits in floating point value

 Which manipulators is used to set only
decimal places digits?
 setprecision prefixed with fixed

 showpoint
 when set, show trailing decimal point and zeros
 showpos
 when set, show the + sign before positive numbers
 fixed
 use fixed number of digits
 scientific
 use "scientific" notation
 adjustfield
 left
 use left justification
 right
 use right justification
 Internal
 left justify the sign, but right justify the value

Manipulators as member function
.precision ( ) ;
 Select output precision, i.e., number of significant
digits to be printed.
 Example:
cout.precision (2) ; // two significant digits
.width ( ) ;
 Specify field width. (Can be used on input or
output, but only applies to next insertion or
extraction).
 Example:
cout.width (4) ; // field is four positions wide

More Input Stream Member Functions
.get ( ) ;
Example:
char ch ;
ch = cin.get ( ) ; // gets one character from
keyboard
// & assigns it to the variable "ch"
.get (character) ;
Example:
char ch ;
cin.get (ch) ; // gets one character from
// keyboard & assigns to "ch"

.get (array_name, max_size, delimiter) ;
Example:
char name[40] ;
cin.get (name, 40,’ ’) ; // Gets up to 39
characters
// and inserts a null at the end of the
// string "name". If a delimiter is
// found, the read terminates. The
// delimiter is not stored in the array,
// but it is left in the stream.

.getline (array_name, max_size, delimiter) ;
Example:
char name[40] ;
cin.getline (name, 40,’ ’) ; // Gets up to 39
characters
// and inserts a null at the end of the
// string "name". If a delimiter is
// found, the read terminates. The
// delimiter is not stored in the array,
// but it remove delimter from stream.

.ignore ( ) ;
Ex:
cin.ignore ( ) ; // gets and discards 1 character
cin.ignore (2) ; // gets and discards 2 characters
cin.ignore (80, 'n') ; // gets and discards up to 80
// characters or until "newline"
// character, whichever comes
// first

Type Cast Operator
 C++ permits explicit type conversation of
variable or expression.
 Function call notation
 (type-name) expression // c notation
 Type-name (expression) //C++ notation
 Example:
 Avg=sum/(float)n; // c notation
 Avg=sum/float(n); // C++ notation
 Only use if expression is an simple identifiers
 Example:
 P=int * (q) //illegal
 P=(int *) q;

Type Cast Operator
Alternatively use typedef to
create identifier
Example
 typedef int * int_pt;
 p=int_pt(q);
 ANSI C++ add following new cast
operators:
 const_cast
 static_cast
 dynamic_cast
 reinterpret_cast

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