Constants

 Constant is a value that can not be changed during execution of program.

Integer constants :

• Consists of numeric digits .
• An integer constant must have at least one digit.
• It can have positive ( + ) or negative ( - ) sign, but the default sign is positive.
• Other than a positive or negative sign, it can not have any special character like decimal point, comma or blank space.

1. Decimal constants : Decimal number system uses numbers from 0 to 9 . In decimal integer                constant first digit can not be 0. For example : 3000, 289 etc.

  

2. Octal constants : Octal number system uses numbers  from 0 to 7. In octal integer constant first  digit must be 0. For example : 0300, 0275 etc.

3. Hexadecimal constants :  Hexadecimal number system uses numbers from 0 to 9 and character from A, B, C, D, E, F, a,b,c,d,e,f. In hexadecimal integer constant first two characters should be 0x or 0X.. For example : 0XA15C, 0xFFA , 0xbe etc.

Real Constants :

Real constants are also called floating point constants. Real constants could be written in two forms :

1. Fractional form

2. Exponential form

1. Fractional Form :

• A real constant must have at least one digit.
• It must have one and only one decimal point.
• It can have a positive or negative sign but the default sign is positive.
• Other than positive or negative sign and a decimal point, a real constant can not have any special character.
• Examples :  + 325.34 ,  426.0 ,  -32.75

2. Exponential form :

• A real constant in this form has two parts - mantissa and exponent.
• The mantissa and exponent part should be separated by a letter E or e .
• The mantissa part may have positive or negative sign but the default sign is positive.
• The exponent must have at least one digit , which must be a positive or negative integer. Default sign is positive.
• Range of real constants expressed in exponential form is  -3.4E38 to 3.4E38.
• Example : 3.2E-5 , -0.61e-5 etc.

Character constants :

A character constant is single alphabet , a single digit or a single special symbol enclosed within single inverted commas.The maximum length of character constant can be one character. For example :  'A'  ,  '@'  ,  '9'  etc.