Elementary Data Types

Variables and Constants

Variables: A variable is it Quadruple which is composed of a name,a set of attributes, a reference and a value.

A simple variable is an elementary data object with a name and binding of data object to value may change during its lifetime. This data objects are basically defined and named by programmer explicitly.

Attribute of a variable:

Lets take example of variable in "ALGOL Language"

y:=9;

We can say that it has four attributes

• 1) the name of the box:y

2) The name of description of a current contents.

i.e 9 we can also say that square of 3.

• 3) the box or storage location(s) which holds(s) the value.

4) the content of the box or 9.

The name of the box and its storage location are fixed, but the contents and it name may vary over time.

Four_components_of_a_variable

Let's take another example in C language:

int N;- It declares a simple data object N of type integer.

N=27; beta value 27 is assigned to variable N.

• 1) declare the variable name N of type integer.

• 2) lifetime of N is execution end.

• 3) data object bound to N during end of execution time.

• 4) value 27 is assigned and may be changed during life of N.

• 5) hidden from the programmer are other binding made by virtual computer like creating Activation Record, Storage for this activation record in Run-TimeStack etc.

08- Elementary Data Type-Variables- Programming Languages




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