1. Constant: value does not change
Variable: a memory location whose contents can vary; also called an identifier
Each programming language has it own rules for naming identifiers, including:
Legal characters
Maximum length
Use of upper or lower case
Variable name must be a single word, but can be formed from several words
rate, interestRate, interest_rate
Constant: value does not change
Values that do not change while the program is running
Have identifiers, and can be used like variables for calculations, but cannot be assigned new values
Literal: is use of data itself (ex: pi – )

2. Variables, Constants and Literals
Variable: Name of a collection of memory cells that are treated as a unit. Contains data that can be changed by the programmer. A container for data that can be changed.
Constant: A named data item that contains information that the programmer does not change. The information stays the same throughout the program execution. A container for data that does not change.
Literal: A constant whose name is the written representation of its value. Example: add 50 to total_accumulator

3. Variables, Constants and Literals
Variables: Contains data that can be changed
- OR -
Container

4. Variables, Constants and Literals
Constant: Contains data that can NOT be changed
- OR -
- OR -
Container of Milk

5. Declaring Variables Assign identifiers to memory locations
Specify the name and data type
Use meaningful names and follow standards
Prefixes may be used to group related variables
Declare a variable for each field in a data file

6. Declaring Variables
Initializing (or defining) the variable: providing an initial value
Some languages provide default initial values
Other languages leave variables with an unknown or garbage value
Variables representing data fields in files do not need to be initialized

7. Declaring Variables Local variables: declared within a module
Global variables: declared at the beginning of the program, and used in all modules
Annotation box: flowchart symbol containing notes
Data Dictionary: list of variables used in a program, with their type, size, and description