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C Constants ?

A constant is a value which will not change during the execution of a program.

Constants are those values in programming language which cannot be modified once they are defined. They are fixed values in a program.

In C program we can define constants in two ways as below:-

  1. Using #define preprocessor directive:- This directive is used to declare an alias name for existing variable or any value.
    Example:-#define identifierName Value.

  2. Using a const keywords:- using const keyword to define constants is as simple as defining variables, the difference is you will have to precede the definition with a const keyword.
  3. Example:-const int var = 5;

Types of C Constants:-
  1. Integer Constant:- An integer is a whole number without any decimal point or a fraction part. No extra characters are allowed other than ‘+’ and ‘-‘ sign.
  2. The integer Constants are divided into three types:-
    • Decimal (10, 140, -140 etc.)
    • Octal(010, 0140, 0440 etc.)
    • Hexadecimal(0x8A, 0xAB, 0xA123)

  3. Enumeration Constants:- A set of named integer constants( The name given to integer constants) defined using the keyword enum are called enumeration constants.
    enum identifier{enumeration-list};
    enum boolean {NO, YES};

  4. Floating point constant:- The floating point constants are base 10 numbers with fraction part such as 10.5. All negative numbers should have a prefix ‘-‘. A positive number can have as optional ‘+’ sign. No other extra characters are allowed.

  5. Character Constant:- A symbol enclosed within a pair of single quotes(‘apostrophe denoted by the symbol’) is called a character constant.

  6. String Constant:- A sequence of characters(i.e., one or more characters)enclosed within a pair of double quotes is called a string constant.