Variables

A program variable is a language abstraction for an area of memory in which data is stored.  Variables are characterized by name, address, type, value, scope, and lifetime.

• Variables are case sensitive - that is, upper case letters are considered to be different from the corresponding lower case letters in identifiers and keywords. 
• Reserved words cannot be used as identifiers.
• There is no limit to the length of variables, but:
• For ANSI C (1989) and before, only the first 31 characters are significant.
• For ANSI C (1999) and after, only the first 63 characters are significant.

• The name of a variable is an identifier.
• Variable names are case sensitive.
• Reserved words cannot be used as variable names.
• Variables can also be anonymous; that is, they have no name.  Anonymous variables are referenced by pointers.

• Variables can be bound to an address statically, dynamically, or programmatically. 
• Static variables are bound to storage locations when they are declared.
• Dynamic variables are bound to storage locations when the block in which they are declared is entered.
• Programmatically controlled variables are bound to storage locations by the malloc() or calloc() functions.  Programmatically controlled variables are anonymous.

• All Variables are statically typed. 
• All Variables must be declared, with an explicit type. 

• Variables declared at the file level (outside of functions) are global.
• Variables declared within blocks are local to that block, and are visible from their declaration to the end of the block.

• File level (global) variables are static by default.
• Local variables are automatic by default.
• Local variables can be declared as static.
• Static variables exist during execution of the program.
• Automatic variables exist from entry of their block to exit from the block.
• Programmatically controlled variables exist from their allocation with malloc() or calloc() until they are deallocated with free.

• variable

  A named data container which can be both read and written in a program.

• A variable can be described as:
  • A named storage location that can contain data that can be modified during program execution
  • A language object that may take different values, one at a time
  • A letter or other symbol used to represent a quantity.
  • A name that may be bound to a value.
  • A named item of data.
  • A symbol denoting a quantity or symbolic representation.
  • A name used to represent data that can be changed while the program or procedure is running.
• Variables are statically typed; the type of a variable must be designated in the code.

• Reserved words cannot be used as identifiers.
• Syntactic keywords are all reserved words.
• Variables must be declared.

• MonthlyTotal
• FirstName
• transaction_amount