What is Constants

What is Constants in C?

Constant is a value that cannot be changed during execution of the program. Constant is user define value, which is input by the user and cannot be changed during the program of execution.

There are three type of constants-

1.        Numeric Constants : Numeric Constants are those constants which consist of digits, they may or may not have decimal point(.).

•   Numeric constant should have at least one digits.

•  No comma or space is allowed within the numeric constant.

•  Numeric constants can either be positive or negative but default sign is always        positive.

•   Decimal constants: e.g. 0,1,2,3,4,5,6,7,8,9. its base is 10. 

•   Octal constants:   e.g. 0,1,2,3,4,5,6,7. its base is 8.

•   Hex decimal : e.g. 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,a,b,c,d,e,f. its base is 16.

    3. String constant : A string constant has zero, one or more than one character. A string constant is enclosed within double quotes (" "). At the end of string,\0 is automatically placed by the compiler. Some example of String constants are-
           "blog"

       Rules for defining numeric constants-

  There are two type of numeric constants-

          Integer constant : Integer constants are whole numbers which have no decimal                   point (.). There are three type of integer constants based on different number   systems. 

           Some valid decimal integer constants are -

              0

              123

              1234

              908654

              34456778

           Some invalid decimal integer constants are-

              2.3                illegal character(.).

              4#33             illegal character #.

              0444             first digits cannot be zero.only zero should be.

              123 4            space not allow.

              4,545            Comma is not allowed.

           in Octal integer constants, first digits must be 0. e.g.

               0

               01

               03

               0453

           in hexadecimal integer constants, first two characters should be 0x or 0X . eg.

                0x

                0x23

                0x333

                0xA4F1

            By default the type of an integer constants is int.But if the value of integer constants               exceeds the range of value represents by int type, the type is taken to be unsigned               int or long int. 

              e.g.  45235                      Integer constants of type int

                      45456566UL            integer constants of type unsigned long int.

                      6655U                     type of unsigned of int.

               

                I will explain about number System our next blog....

           Real Constants: it is also called floating constants. Floating constants are numeric               constants that contain decimal point. if decimal constant number have  point(.) that                called floating number. some valid floating point constants are-

                0.5

                4.4

                3000.0

                34.89

            for expressing very large or very small real constants, scientific(exponent) form is                  used.in example, number is written in the mantissa and exponent form,which are                  separated by 'e' or 'E'. The mantissa can be an integer or real number, while the                   exponent  can be only an integer (positive or negative). for example 1800000 can                  be written as 1.8e6, here 1.8 is mantissa and 6 is exponent.

             some other example: 2500000000 we write 2.5e9 or 2.5*1000000000

             by default the type of a floating point constant is double.the symbol for recognizing                 is f or F (for float type) l or L( for Long double).

                 2.3e5                floating point constant of type double

                2.4e-9L              floating point of type long double.

                3.5f                    floating point of type float..

    2. Character constants:  A  character constant is a single character that is enclosed                within single quotes.Some valid character constants are-

         

          '3'          'A'          '$'          ' '          '#'

      Some invalid character constants are-

      

      'four'              there should be only one character within quotes.

      "A"                 double quote are not allowed 

       a                   single quote is missing.

   

       ''                   no character between single quotes at least space should be.

  

    Every character constant has a unique integer value associated with it. This integer is the numeric value of the character in the machine's character code. if the machine is using ASCII code then the character 'G' represents integer value 71 its means that if we write 71 it is a equal to 'G' and character 5 represent 53.

   

              ASCII value is 

      

         A - Z                        ASCII value (65 -90)

         

         a - z                         ASCII value (97 -122)

         0 -9                          ASCII value (48 - 57)

         ;                                ASCII value (59)

           "342"

           "3"

           " "

           "i"