2008-2-41CSE 3302 Programming LanguagesData TypesChengkai Li, Weimin HeSpring 2008Data TypesLecture 7 – Data Types, Spring 20081CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 2008Data Types• What is a data type?A name with certain attributes:– The values that can be stored, the internal representation, the operations, …• A data type is a set of values• e.g., int in Java:int x;x∈Integers= [-2147483648, 2147483647]• A data type is also a set of operations on the valuesLecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 20082Why are data types important?• Example: z = x / y; (Java)– int x, y; x=5; y=2;• Integer division, x/y results in 2.•int z: z=2;int z: z 2;• double z: z=2.0;– double x, y; x=5; y=2;• floating-point division, x/y results in 2.5• int z: wrong!• double z: z=2.5;Lecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 20083Java Types Primitive Reference Lecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 20084Type structure of JavaNumericclass interface double boolean short Integral float Floating point int char Array long byte C Types Numeric Pointer Function struct union void Basic Derived Array Lecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 20085double long double short int Integral float Floating enum int char (signed) (unsigned) long int Type structure of CSimple Data Types• No internal structure:e.g., integer, double, character, and boolean.• Often directly supported in hardware.– machine dependencyMdfid il•Most predefined types are simple types.– Exceptions: String in Java.• Some simple types are not predefined• Enumerated types• Subrange typesLecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 200862008-2-42Enumerated TypesOrdered set, whose elements are named and listed explicitly.• Examples:enum Color_Type {Red, Green, Blue}; ( C )tClTi(RdG Bl)(Ada)type Color_Type is (Red, Green, Blue); ( Ada )datatype Color_Type = Red | Green | Blue; ( ML )• Operations: ?Successor and predecessorLecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 20087Ada Exampletype Color_Type is (Red, Green, Blue);x : Color_Type := Green;x : Color_Type’Succ(x);x : Color_Type’Pred(x);put(x); -- prints GREEN• No assumptions about the internal representation of values• Print the value name itselfLecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20078Pascal Exampletypecardsuit = (club, diamond, heart, spade);card = recordsuit: cardsuit; value: 1 .. 13; end; varhand: array [ 1 .. 13 ] of card; • Succ(diamond) = heart; Pred(spade) = heart;• club < heart; is true.• for acard := club to heart doLecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20079C Example#include <stdio.h>enum Color {Red, Green, Blue};enum Courses {CSE1111=1, CSE3302=3, CSE3310=3, CSE5555=4};main() {enum Color x = Green;enum Courses c = CSE3302;x++x++;printf("%d\n“,x);printf("%d\n",Blue+1);printf("%d\n",c);return 0;}• Enum in C is simply int• Can customize the valuesLecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200710Java Examplepublic enum Planet { MERCURY (2.4397e6), EARTH (6.37814e6);private final double radius; // in meters Planet(double radius) {this.radius = radius; } private double radius() { return radius; } public static void main(String[] args) {p(g[]g){for (Planet p : Planet.values())System.out.printf(“The radius of %s is %f\n", p, p.radius()); } } java.util.Enumeration has different meaningfor (Enumeration e = v.elements() ; e.hasMoreElements() ;) System.out.println(e.nextElement());Lecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200711Evaluation of Enumeration Types• Efficiency – e.g., compiler can select and use a compact efficient representation (e.g., small integers)• Readability -- e.g. no need to code a color as a number• Maintainability – e.g., adding a new color doesn’t require updating hard-coded constants.• Reliability -- e.g. compiler can check operations and ranges of value.Lecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200712Courtesy of Charles Nicholas at UMBC2008-2-43C Example for Maintainabilityenum Color {White, Green, Blue, Black};enum Color {White, Yellow, Green, Blue, Black};main(){enum Color x = Black;int i = x;while (i >= White){if (i < Green)if (i < Green)printf(“this is a light color!\n”);i--;}}What if no enumeration?if (i < 1) printf(“this is a light color!\n”);Has to be changed to:if (i < 2) printf(“this is a light color!\n”);Lecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200713Ada Example for Reliabilitytype DAY is (MON, TUE, WED, THU, FRI, SAT, SUN); type DIRECTION is (NORTH, EAST, SOUTH, WEST);GOAL : DIRECTION;TODAY : DAY;START : DAY; TODAY := MON;GOAL := WEST;START := TODAY; TODAY := WEST; -- Illegal: WEST is not a DAY valueTODAY := 5; -- Illegal: 5 is not a DAY valueTODAY := TODAY + START; -- Illegal: "+" is not defined for DAYSLecture 7 – Data Types, Fall 2007CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200714Subrange TypesContiguous subsets of simple types, with a least and greatest element. • Example: type Digit_Type is range 0..9; ( Ada)• Not available in C,C++,Java. Need to use something like:byte digit; //-128..127...if (digit>9 || digit <0) throw new DigitException();• defined over ordinal types:– ordered, every value has a next/previous element• E.g., integer, enumerations, and subrange itselfLecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 200815Type constructors: Defining New Types• Type constructors as set operations:– Cartesian product– Union–SubsetLecture 7 – Data Types, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, Weimin He, 200816Subset– Functions (Arrays)• Some type constructors do not correspond to set operations(e.g., pointers)• Some set operators don’t have
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