1. Data Types

2. Objectives of this session
Basic Data Types
bool & wchar_t
Built-in Data Types
User-defined Data Types
Derived Data Types
Symbolic Constants
Dynamic Initialization of Variables
Reference Variables

3. Variables and Data Types
Tokens
The smallest individual units in a program are known as tokens.
Keywords
Identifiers
Constants
Strings
Operators

4. Keywords

5. Identifiers
A valid identifier is a sequence of one or more letters, digits or underscore characters (_). Neither spaces nor punctuation marks or symbols can be part of an identifier. Only letters, digits and single underscore characters are valid. In addition, variable identifiers always have to begin with a letter. They can also begin with an underline character (_ ).

6. Identifiers The name of a variable:
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The name of a variable:
Starts with an underscore “_” or a letter, lowercase or uppercase, such as a letter from a to z or from A to Z.
Examples are Name, gender, _Students, pRice.
Can include letters, underscore, or digits.
Examples are: keyboard, Master, Junction, Player1, total_grade, _ScoreSide1.
Cannot include special characters such as !, %, ], or $.
Cannot include an empty space.
Cannot be any of the reserved words.
Should not be longer than 32 characters (although allowed).

7. Basic Data Types C++ Data Types User-defined Type Built-in Type
Derived Type
structure
union
class
enumeration
array
function
pointer
reference
Integral Type
Void
Floating Type
int
char
float
double

8. Basic Data Types ANSI C++ added two more data types bool wchar_t
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ANSI C++ added two more data types
bool
wchar_t

9. Data Type - bool
A variable with bool type can hold a Boolean value true or false.
Declaration:
bool b1; // declare b1 as bool type
b1 = true; // assign true value to b1
bool b2 = false; // declare and initialize
The default numeric value of
true is 1 and
false is 0.

10. Data Type – wchar_t
The character type wchar_t has been defined to hold 16-bit wide characters.
wide_character uses two bytes of memory.
wide_character literal in C++
begin with the letter L
L‘xy’ // wide_character literal

11. Built-in Data Types
int, char, float, double are known as basic or fundamental data types.
Signed, unsigned, long, short modifier for integer and character basic data types.
Long modifier for double.

12. Built-in Data Types Type void was introduced in ANSI C.
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Type void was introduced in ANSI C.
Two normal use of void:
To specify the return type of a function when it is not returning any value.
To indicate an empty argument list to a function.
eg:- void function-name ( void )

13. Built-in Data Types
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Type void can also used for declaring generic pointer.
A generic pointer can be assigned a pointer value of any basic data type, but it may not be de-referenced.
void *gp; // gp becomes generic pointer
int *ip; // int pointer
gp = ip; // assign int pointer to void pointer
Assigning any pointer type to a void pointer is allowed in C & C++.

14. Built-in Data Types void *gp; // gp becomes generic pointer
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void *gp; // gp becomes generic pointer
int *ip; // int pointer
ip = gp; // assign void pointer to int pointer
This is allowed in C. But in C++ we need to use a cast operator to assign a void pointer to other type pointers.
ip = ( int * ) gp; // assign void pointer to int pointer
// using cast operator
*ip = *gp;  is illegal

15. User-Defined Data Types
Structures & Classes:
struct
union
class
Legal data types in C++.
Like any other basic data type to declare variables.
The class variables are known as objects.

16. User-Defined Data Types
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Enumerated Data Type:
Enumerated data type provides a way for attaching names to numbers.
enum keyword automatically enumerates a list of words by assigning them values 0, 1, 2, and so on.
enum shape {circle, square, triangle};
enum colour {red, blue, green, yellow};
enum position {off, on};

17. User-Defined Data Types
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Enumerated Data Type:
enum colour {red, blue, green, yellow};
In C++ the tag names can be used to declare new variables.
colour background;
In C++ each enumerated data type retains its own separate type. C++ does not permit an int value to be automatically converted to an enum value.

18. User-Defined Data Types
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Enumerated Data Type:
colour background = blue; // allowed
colour background = 3; // error in C++
colour background = (colour) 3; // OK
int c = red; // valid

19. User-Defined Data Types
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Enumerated Data Type:
By default, the enumerators are assigned integer values starting with 0. We can override the default value by explicitly assigning integer values to the enumerators.
enum colour { red, blue=4, green =8};
enum colour {red=5, blue, green};

20. User-Defined Data Types
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Enumerated Data Type:
C++ also permits the creation of anonymous enum (i.e., enum with out tag name).
enum {off, on}; here off  0 and on  1
int switch_1 = off;
int switch_2 = on;

21. Derived Data Types Arrays Functions
The application of arrays in C++ is similar to that in C.
Functions
top-down - structured programming ; to reduce length of the program ; reusability ; function over-loading.

22. Derived Data Types Pointers
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Pointers
Pointers can be declared and initialized as in C.
int * ip; // int pointer
ip = &x; // address of x assigned to ip
*ip = 10; // 10 assigned to x through indirection

23. Derived Data Types Pointers
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Pointers
C++ adds the concept of constant pointer and pointer to a constant.
char * const ptr1 = “GOODS”; // constant pointer
int const * ptr2 = &m; // pointer to a constant

24. Symbolic Constants Two ways of creating symbolic constant in C++.
Using the qualifier const
Defining a set of integer constants using enum keyword.
Any value declared as const can not be modified by the program in any way. In C++, we can use const in a constant expression.
const int size = 10;
char name[size]; // This is illegal in C.

25. Symbolic Constants const allows us to create typed constants.
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const allows us to create typed constants.
#define - to create constants that have no type information.
The named constants are just like variables except that their values can not be changed. C++ requires a const to be initialized.
A const in C++ defaults, it is local to the file where it is declared. To make it global the qualifier extern is used.

26. Symbolic Constants extern const int total = 100; enum { X, Y, Z };
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extern const int total = 100;
enum { X, Y, Z };
This is equivalent to
const int X = 0;
const int Y = 1;
const int Z = 2;

27. Reference Variables
A reference variable provides an alias for a previously defined variable.
For eg., if we make the variable sum a reference to the variable total, then sum and total can be used interchangeably to represent that variable.
data-type & reference-name = variable-name
float total = 100;
float &sum = total;

28. Reference Variables
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A reference variable must be initialized at the time of declaration. This establishes the correspondence between the reference and the data object which it names.
int x ;
int *p = &x ;
int & m = *p ;

29. When the function call f(m) is executed,
Reference Variables
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void f ( int & x ) {
x = x + 10; }
int main ( )
int m = 10;
f (m);
When the function call f(m) is executed,
int & x = m;