Constant

CONSTANT

There are three type of constants: string constants, numeric constants and character constants.

 Constants    -    string constants

                    -    Numeric constants

                    -    Character constants

String Constants

A String constants is a sequence of alphanumeric characters enclosed in double quotation marks whose maximum length is 255 characters. Following are the examples of valid string constants.

    (1)    ″    the   result = ״

    (2)    ″    Rs 2000.00″  

    (3)    ″    This is test program by Ravic″

Following are some examples for invalid string constants.

Ravichandran                   - Characters are not enclosed in double quotation marks.

“ My name is %$%      - Closing double quotation mark is missing.

‘this is test’                    - Characters are not enclosed in double quotation marks.

Numeric Constants

Numeric constants are positive or negative numbers. There are four types of numeric constants: integer constants, floating point constant, hex constant and octal constants. An stant may either be of single precision or double precision.

                                                         -        Integer

Numeric constants         Integer       -        Short integer integer (short)

                                                         -        Long integer (long)

                                                   

                                          Float       -  ­      Single precision (float)

                                                          -        Double precision (double)

                                                          -        Long double

                                                         -       Unsigned char

                                                         -       Unsigned integer

                                    Unsigned      ­-      Unsigned short integer 

                                                         -       Unsigned long integer

                                             Hex      -        Short hexadecimal l

                                                         -       Long hexadecimal

                                          Octal       -        Short octal

                                                          -        Long octal

(a)   Integer constants  Integer constants do not contain decimal points. Variables can be declared as integers in the following ways.

           int x,y;

           short int x , y ;

           long int  x , y ;

In the first statement, the variables x and y take integer values. In the second statement x, y are of the short integer type. The third statement declares x, y as long integer type variables.

(i )     Integer data : The keyword ‘int’ stands for the integer data type in C++ and its size is either 16 or 32 bits. A 16 bit integer may fall in the range of -2¹⁵  to 2¹⁵ -1, while 32 bits integers may fall in the range of -2³¹ to 2³¹ -1. Integer data type can again be classified into three groups as normal integer , short integer, and long integer types. The normal integer may be either 16 bit or 32 bit long depending upon  the index used by the programmer.

(ii)  Short integer data type : Normally, the ‘short int’ is use to declare the short integer data type in C++ whose maximum size is 16 bits long. It may fall in the range between -32,768 to 32,767 or -2¹⁵ to 2¹⁵ -1.

(iii)  Long integer data type : Usually, the ‘long int’ stands for the long integer data type used in C++ and its size is 32 bits. It may fall in the range of -2,147,483,648 to 2,147,483,647 or -2³¹ to 2³¹ -1.

    The long integer data type declared for reading or writing of the data is identified by an appended “L” or “I”.

(iv)  Unsigned data type : The unsigned numbers are whole numbers and always hold positive values and the sign bit also belong to the value. The unsigned numbers may be classified into four types: unsigned char, unsigned integer, unsigned short integer and unsigned long integer. The maximum size of the unsigned integer is 16 or 32 bits. The unsigned short integer can be denoted as ‘unsigned short int’ in C++ and its size is 16 bits or its range is from 0 to 65635. The using long integer can be declared in C++ as ‘unsigned long int’ whose maximum size is 32 bits or its range is from 0 to 4,294,976,295.

(b)  Floating point constants   positive or negative numbers are represented in exponential form (similar to scientific notation). The floating point constant consists of an optionally signed integer or fixed point number (the mantissa) followed by the letter E and e an optionally signed integer (the exponent).

Examples

    9010E10

    7810.11E-11

    -10.990e8

    -1.001e-1

(i)   Floating data type: The number which are stored in the from of floating point represented with binary mantissa and exponent are known as floating point numbers. They can be declared as ‘float’ in C++ whose maximum size is a rational number approximately between -0.29e-38 in C++.

(ii)  Double data type : ‘double’ is a keyword to represent double precision floating point numbers in C++. The size of  ‘double’ is a rational number in the same range as float and is stored in the form of floating point representation with binary mantissa and exponent.

The typical floating point types and its size in C++ are given in the following table:

Data Type	Size in Bytes
float double long double	4 8 12 or 16

    

                                              

(c)  Hex constants   Hexadecimal numbers are numbers are integer number of base 16 and their digits are 0 to 9 and A to f ( a to f ). Any hexadecimal number is characterized in the  is Hex Constants group. In C++ , it is normally represented using character x.

     Here are some examples

          0x0

          0x3

          22x3

(d)  Octal constants  Octal numbers are integer numbers of base 8 and their digits are 0 to 7. Any octal number is characterized in the octal constants group.

     The typical integer data types and its sizes in C++ are given in the following table:

Data Types	Size in Bytes
char short int long	1 2 2 or 4 4 or 8

Character Constants

A character represented within single quotes denotes a character constant.

   Here are some examples,

 ‘A’

 ‘a’

 ‘:’

 ‘?’

Character data type  Any character belonging to the ASCII character set is considered as a character data type whose maximum size is 8 bits long. The char is keyword to   represent the character data type in C++. Character constants are always represented within single quotes. Plain char, signed char and unsigned char are three distinct types. A char, signed char and unsigned char are three distinct types. A char, a signed char and an unsigned char occupy the same amount of memory space. The classification of the char data type is dependent on the version of the C++ compiler.

Declaration of the character constant

   char x;

   char x, y, z;

The char stands for the character data for declaring the character constants. The declaration format of character data type is same as that of the declaration of integer, floating or string constants.

The backslash (\) is use to denote non-graphic characters and other special characters for a specific operation. The flowing characters are used as non-graphic characters:

 ‘\a’                                 alert bell character

 ‘\n’                                 newline (line feed)

 ‘\t’                                  horizontal tab

 ‘\b’                                 back space

 ‘\r’                                  carriage return

 ‘\f’                                  form feed

 ‘\v’                                 vertical tab

 ‘\\’                                  back slash

 ‘\’’                                  single quote

 ‘\0’                                  mull character

  ‘\?’                           question mark

 ‘\000’                             octal value such as \o33

 ‘\xhhh'                            hexadecimal value such as \x1b]

Note that the null character ‘\0’ is to be distinguished from 0 (zero, not the alphabet ‘o’)

The following table summarize the data types in C++

Name	Meaning
char int long int short int unsigned char unsigned int unsigned short int unsigned long int float double	character integer long integer (more digits) short integer (fewer digits) unsigned character unsigned integer unsigned short integer unsigned long integer floating point number double precision floating point number