Constant and Variable In C

  

Constant:

This value has one or more decimal digits and can be positive or negative; the decimal point is optional. The value remains the same regardless of the decimal digits. This value is a constant value that is maintained in memory and cannot be changed.

For ex. 11,2.16,-12,-3.12 etc.

 

The two main categories of C Constant are:

1) Primary Constant.

2) Secondary Constant.

 1) Primary Constant:

   a)Integer Constant:

      The term "integer constant" simply refers to a constant number without a decimal point that can be either positive or negative.

Ex: 1456, 52,-652,-3

 

    b)Real Constant:

        Floating point constants are also known as real constants. Real constants are numerical values that can be expressed in two different ways: fractionally and exponentially.It could be either favourable or unfavourable.

Ex: 14.5, 1.34, -12.654, 4.1e8

 

    c)Character Constant: 

       A single alphabet, one digit, or one unique special symbol enclosed in a single inverted comma constitutes a character constant. One character is the maximum length for a character constant.

Ex: 'A', '2', 'd'

 

 2)Secondary Constant:

   a)Array:

      An array is a group of related elements kept in a single area of memory.

Ex: a[5].

 

   b)Pointer:

      To point to a certain data type, a pointer must be defined.

Ex: int*n, float*rate.

 

   c)Union:

       Union and structure are equivalent syntactically. A union element can be accessed in the same way as a structural member. A union offers a technique to take multiple perspectives of the same memory locations.  

    d)Enum:

       A data type that has user-specified values is an enumerated data type.

Ex: the declaration

     enum city{Aurangabad,Pune,Nagpur};

     To define a variable of type enum city,  write enum   city name;

 

Variable:

A variable is a value that could change while the programme is running. This value is kept in memory as a variable that can be called by its name to access it. A memory location is only symbolically represented by a variable name.                        

Ex: int math mark=96

Here, the math mark is a variable of integer type. The variable is assigned value:96.

 

Rules for constructing Variable Name:

1)Any alphabetic, numeric, or underscore combination can be used as a variable name. The name of the variable has no length.

2)The variable name must begin with an alphabetic character or an underscore.

3)A variable name cannot contain any commas or spaces.

4)32 reserved key words are not allowed in variable names.

5)The only special character that can be used in a variable name is an underscore.