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• Elementary Types : Values are
logically indivisible
• Composite Types : Values composed
from components
Type Classification
Elementary
Types
Scalar
Types
Access
Types
Discrete
Types
Real
Types
Scalar Types
→ relational operators are
defined
position number
Scalar
Types
Discrete
Types
Real
Types
Integer
Types
Enumeration
Types
Fixed
Point
Floating
Point
• Ordered
• Each value of a discrete type has a
Attributes of Scalar Types
range of S. The value of this attribute
is of the type of S.
range of S
Operations on Scalar Types
the value in the type
string
on the scalar type
– S’Succ (Integer) : returns (Integer + 1)
S’First denotes the lower bound of the
S’Last denotes the upper bound of the
S’Range is equivalent to the range
S’First .. S’Last
S’Min returns lower of two elements
S’Max returns higher of two elements
S’Value accepts a string and returns
S’Image converts the value into a
S’Pred and S’Succ – behavior depends
S’Pred (Integer) : returns (Integer -1)
Subtypes
subtype Natural is Integer range 0..Integer’Last;
subtype Positive is Integer range 1..Integer’Last;
subtype NonNegativeFloat is Float range 0.0 .. Float’Last;
subtype SmallInt is Integer range -50..50;
subtype CapitalLetter is Character range ’A’..’Z’; X, Y, Z : SmallInt; NextChar : CapitalLetter; Hours_Worked : NonNegFloat;
X := 25;
Y := 26;
Z := X + Y;
Operations on Discrete Types
of the argument
whose position number equals the
value of S
S’Pos(Arg) returns the position number
S’Val(Arg) a value of the type of S
CQ
Enumeration Types
type Class is (Freshman, Sophomore, Junior, Senior);
type days is (Mon, Tue, Wed, Thu, Fri, Sat, Sun); type colours is type traffic_colours is (green, yellow, red); type suits is (clubs, diamonds, hearts, spades);
words
• The outputs are exactly the same
• There will be no outputs
• The outputs are different
• I don’t know
(white, red, yellow, green, blue, pink, black);
• A data type whose values are a collection of allowed
Derived Types
• age := -20;
• shoe_size := 2 * no_on_bus;
real world.
Derived Integer Types
• derived from INTEGER:
• type ages INTEGER range 0 .. 110;
age : ages;
voting_age : constant ages := 18;
type heights 0 .. 230;
height : heights;
min_enrolment : constant := 6;
max_enrolment : constant := 200;
type class_sizes 0..max_enrolment;
class_size : class_sizes;
height := age - class_size;
• Types help program values reflect the
New data types can be
is new
is range
is range
Type conversion
strong typing: different types cannot
be mixed
- type length 5 range 0.0 .. 1.0E10;
type area 5 range 0.0 .. 1.0E20;
function area_rectangle (L,H : length) return area is
begin
return area(L) * area(H);
end ;
Benefits of derived types
– age := -20;
– class_size := class_size + 100;
objects
• Ada has
• Explicit type conversion is permitted:
is digits
is digits
• Nonsense rejected by compiler
height := age - class_size;
• "Out of range" rejected by compiler
• “Out of range” run time error
• Enforce distinct nature of different
• Robust, elegant, effective programs
Example
• subtypes[1..3].adb
