The ones who are crazy enough to think they can change the world are the ones who do.- Steve Jobs

Constant variable, does not change its value during the execution of a program. A constant is a data value written by a programmer. Constants may be belonging to any of the data type(int, float, char). There are **4** basic types of constants. They are

- Integer Constant.
- Floating Point Constant.
- Character Constant.
- String Constant.

- An integer constants consists of sequence of Integer numbers from
**0 to 9**. - Decimal points, black spaces, commas cannot be included within an integer constants.
- An Integer constants can either be positive or negative or zero.
- The number without sign can be assumed as positive
- Integer constants can be classified into
**3**ways . They are - Decimal Integer Constants.
- Octal Integer Constants.
- Hexadecimal Integer Constants.

A Decimal integer constants consist of any combination of digits from 0 to 9. A Decimal integer constants can contain two or more digits, but first digit should not be 0. Base value of decimal integer is 10.

0 | 12 | 856 | 456844 |

45,565 | invalid character (,) |

25.0 | invalid character(.) |

1 2 3 | invalid character(blank space) |

12-23-34-456 | invalid character(-) |

051 | first digit cannot be a zero |

An Octal integer should starts with 0 in order to identify the constant as an octal integer number. An Octal integer constants consist of any combination of numbers between 0 to 7. Base value of Octal integer constants is 8.

0 | 012 | 0856 | 0456844 |

4725 | does not starts with 0 |

01491 | invalid digit(9) |

012.23 | invalid character(.) |

051-43 | invalid character(-) |

A Hexadecimal integer constants can be a combination of any numbers in the range of 0 to 9 and a to f or A to F. Here A to F denotes 0 to 15. A Hexadecimal integer constants should starts with either 0x or 0X. Base value of Hexadecimal integer constants is 16.

0x | 0X12 | 0x8A6 | 0x4a84b4 |

4725 | does not starts with 0x |

0x1H9 | invalid charcter(H) |

0X12.23 | invalid character (.) |

0X51-43 | invalid character(-) |

Unsigned or Long Integer Constants may exceed the range of Integer. Unsigned or Long Integer Constants are identified by the suffix u or l. Here

- u represents unsigned int.
- L represents long int.

4541U | unsigned int |

4558L | long int |

A floating point constant consist of integer part, decimal point and fractional part. A floating point constant contains exponential field e or E followed by an integer. A normal decimal point value will be treated as double until a suffix f is added to the decimal point value. Decimal point value using double will be more accurate than float. Adding suffix l or L to the Decimal point value will be treated as long double. A floating point constant with an exponent is essentially the same as scientific notation, except that base 10 is replaced by e or E. Exponential notation is useful in representing the numbers whose magnitudes are very large or very small.

Valid Floating Point Constants | Invalid Floating Point Constants |
---|---|

47.00 | 47 |

0.4 | 0 5 |

Consider the number 257.47. This can also be return as 0.25747E^{3}. The sequence of digits after decimal point (25747) is a mantissa. The power of E (3) is known as exponent.

Valid Exponential notation | Invalid Exponential notation |
---|---|

542.254E^{6} |
7.5.3E^{4} |

542.254e^{6} |
7.5.3e ^{ 4} |

A character constant is a single character enclosed within single quotes **' '**. A character constant also represented with a single digit or a single special character or white space enclosed within a single quotes. All PC make use of ASCII(American Standard Code for Information Interchange) character set, where each integer character is numerically encoded. A character constant occupies a single byte.

Valid Character Constants | Invalid Character Constants |
---|---|

'a' | 'ab' |

'1' | '22' |

A string constant is a sequence of characters enclosed within double quotes **" "**. The Characters may consists of letters, digits, escape sequences and spaces. A string constant always ends with null (/0). A string constant occupies a two bytes.

Valid String Constants | Invalid String Constants |
---|---|

'Hello Programmer' | 'Hello Programmer" |

"Hello Programmer" | "Hello Programmer' |

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