Basic Types & User Defined Types

Transcription

1 Basic Types & User Defined Types 1. Objectives Built-in Types and Primitive Types Data Aggregates and Type Constructors Constructors User-defined Types and Abstract Data Types... 7 A. Bellaachia Page: 1

2 1. Objectives How to structure your data? How to organization your data? How to use primitive types to build user-defined types? How types are implemented? 2. Built-in Types and Primitive Types What is a type? Values Operations A primitive type mimics hardware units. We call primitive types those types that are not built from other types. Example: Character is a primitive type in C, but String is not. Boolean is not a primitive type in C while it is in Java. Examples: Booleans Integers Reals Characters Benefits: Hides underlying representation A. Bellaachia Page: 2

3 Can do type checking at compile time Can resolve overloaded functions at compile time Programmer can specify the accuracy required 3. Data Aggregates and Type Constructors Definition: An aggregate data type, also called compound object, consists of one or more data type objects. Example: o Arrays: consists of one or more elements of a single data type placed in contiguous locations from first to last. Constructors: It is the method used to create an aggregate data type. Examples: o Cartesian Products o Sequences o Etc. 4. Constructors Cartesian Product: A constructor used to create records and structures Definition: Cartesian product of n sets A1, A2, A3,, An is a set whose elements are ordered n-tuples (a1, a2, a3,, an), where each ak belongs to Ak for 1 k n. Example: A. Bellaachia Page: 3

4 o Structure in C o Records in Pascal and Ada. o A C example: #include <stdio.h> typedef struct { char name[30]; int age; char ssn[10]; person; main (){ person myname = {"Bell", 20, " "; printf("person Info: \n"); printf("\t\t%s\n\t\t%d\n\t\t%s\n", myname.name,myname.age, myname.ssn); Mapping Definition: o A mapping is a function from a set of values (domain) to a set of values (range): F: integer -> real Array Constructor: is a mapping from a set of integers (index) to a set of values (content of the array). A. Bellaachia Page: 4

5 Example: o Int myarray[5] ={-2,0,-3,4,300; Another Example: MyArray: 0-2 MyArray: 1 0 MyArray: 2-3 MyArray: 3 4 MyArray: enum Colors {red, white, black, green, blue; The compiler assigns an integer number to each name in the enumerated type starting from zero. Union and Discriminated Union Union is a constructor that allows objects to be specified by a disjunctive of fields, e.g., field 1 or field 2 or... or field n. An instance object has only one field: Save space. It is up to the programmer to remember which address is valid Example: o Variant records in Pascal o Union structures in C: union mixed { int i; A. Bellaachia Page: 5

6 ; float f; char c; union mixed m; m.i = 10; Powerset: Powerset(T): This is a constructor that creates a variable whose value is a set of elements of type T. T is called the base type. Example: o set type in Pascal o Java APIs: Sets. Sequence: Sequences constructor allows the creation of objects whose number of elements is not specified. Objects will have arbitrary size. Example: sequential files, Vector, List in Java. Recursion Recursion is a constructor that allows the size of an object to grow dynamically (add or delete elements). Example: Create the structure of a Linked List in C typedef strcut { A. Bellaachia Page: 6

7 DoulyLinkedList * previous; Char name[30]; DoulyLinkedList * next; doublylinkedlist; doublylinkedlist *head; 5. User-defined Types and Abstract Data Types The ability to create new data types using primitive data types. Example: typedef struct { int numerator; int denominator; fraction; Define variables of type fraction: fraction f1, f2; Abstract Data Type (ADT) It is an extension to the record or structure construct: Plus routines C++/Java: ADT is a class construct. Constructor: It allocates and initializes the fields of an ADT. Languages usually provides a default constructor and default initializations. A. Bellaachia Page: 7

8 Deconstructor: Example: C++ class fraction{ public: o It releases the memory allocated for an instance. o C++: a deconstructor has the name of the class prefixed by ~ o Java: provide a garbage collector to clean memory allocated by an object. fraction (int i, int j){ numerator = i; denominator = j; fraction (){ numerator = 0; denominator = 0; fraction mul (fraction f1, fraction f2){ fraction f(0,0); f.numerator = f1.numerator * f1.numerator; f.denominator = f1.denominator * f1.denominator; return (f); print (){ cout << numerator/denominator; private: int numerator; int denominator; A. Bellaachia Page: 8

9 Generic ADT: An ADT that takes data types as parameters. C++ : template. Example: ( // Create a template function that returns the // greater one of two objects we could use: #include <iostream.h> template <class T> T GetMax (T a, T b) { T result; result = (a>b)? a : b; return (result); int main () { int i=5, j=6, k; long l=10, m=5, n; k=getmax<int>(i,j); n=getmax<long>(l,m); cout << k << endl; cout << n << endl; return 0; A. Bellaachia Page: 9