Types and Variables

1
Types and Variables

• A type is simply a template for what a variable
  in memory will look like. Declaring a type does
  not allocate memory for storage.
• A variable is a named location in memory that has
  been declared to contain a particular type of
  data.

2
Ada Predefined Types

• Boolean (true or false)
• Integer (whole numbers e.g. 1,2,-3)
• Float (real numbers e.g. 1.12, -0.37)
• Character (any ASCII character e.g. a, b, tab)
• String() (a string of characters of length )
• Natural (non-negative integers)

3
Variable Declarations

• Examples
• flag boolean -- can be either true or false
• number integer -- can be any whole number
  -- including negative numbers
• realnum float -- can be any real number
• -- including negative numbers
• somechar character -- can be any ASCII
  character
• somestring string(1..20) -- is a string of 20
  characters
• Reminder
• number constant integer 10 -- creates a
• -- memory location named number with the value
  10 that -- cannot be changed

4
User Defined Subtypes

• Form
• Subtype typename is basetype in range
  start..stop
• Where typename is the name of the subtype (e.g.
  age_type)
• basetype is the name of the original type (e.g.
  integer)
• start is a starting position for the range
  (e.g. 0)
• stop is a stopping position for the range (e.g.
  130)
• Example
• Subtype age_type is integer range 0..130

5
Enumerated Types

• Form
• Type typename is (list of elements)
• Where
• typename is the name given the type (e.g.
  gender_type)
• list of elements is the list of type members
  (e.g. male, female)
• Example
• Type gender_type is (male, female)

6
Enumerated Types (cont.)

• Enumerated types can be used in input and output
  by instantiating and using a predefined Ada
  package.
• Package gender_io is new ada.text_io.enumeration_i
  o(enumgt gender_type)
• Given that gender is of type gender_type, you may
  then use
• gender_io.put(itemgtgender)
• gender_io.get(itemgtgender)

7
Type Attributes

• All data types have predefined attributes
• typefirst is the first element of the type
• typelast is the last element of the type
• typepos(value) returns the position within the
  type of a given value
• typeval(pos) returns the value in a particular
  position of the type
• typepred(value) returns the predecessor of the
  given value within the type
• typesucc(value) returns the successor of the
  given value within the type

8
Type Attributes (cont.)

• Given the type declaration
• Type group_type is (Mary, Bob, Carl, Kelly)
• group_typefirst is Mary
• group_typelast is Kelly
• group_typeval(1) is Bob (note position numbers
  start with 0)
• group_typepos(Carl) is 2
• group_typepred(Bob) is Mary
• group_typesucc(Carl) is Kelly
• IMPORTANT pred of the first element and succ of
  the last element are undefined!!