Machine architecture and programming languages
�      Programming languages reflect the underlying gadget
�      Modern computers use van Neumann architecture
�    There are  number one additives
�   Memory, which shops each this system instructions and the records
�   The processor, which offers instructions to adjust the facts in memory
�      In a programming language,
�    The abstractions for the memory cells are the variables
�    The abstractions for the processor are functions
 

Fundamental issues of variables
�      The attributes of variables
�    Name
�    Address
�    Type
�    Value
�    Lifetime
�    Scope
 
�      Concepts involving variables
�    Alias
�    Binding instances
�    Type Checking
�    Strong typing
�    Type compatibility
�    Static & dynamic scoping

Names � a fundamental attribute of variables

�      Design issue of the programming language

�   Should the names be case sensitive?

�   Should special names be reserved words or keywords?

�   A keyword can be used by the programmer as an identifier.

�   A reserved word cannot.

�   How many characters are allowed in a name?

�   Which characters should be allowed in names?

Addresses � another fundamental attribute of variables

�      The address of a variable is the memory address with which it is associated.

�    This association is made in the symbol table for static variables.

�      In some languages it is possible for the same name to be associated with different addresses at different time in the program

�    Different subprograms may have local variables with the same name

�      It is also possible to have multiple variables associated with the same address

�    The variables that access the same memory location are called aliases