1. 1 Chapter 11- 2 Structured Types, Data Abstraction and Classes Dale/Weems

2. 2 Hierarchical Structures l The type of a struct member can be another struct type l This is called nested or hierarchical structures l Hierarchical structures are very useful when there is much detailed information in each record For example...

3. 3 struct MachineRec Information about each machine in a shop contains: an idNumber, a written description, the purchase date, the cost, and a history (including failure rate, number of days down, and date of last service)

4. 4 struct DateType { int month; // Assume 1.. 12 int day;// Assume 1.. 31 int year; // Assume 1900.. 2050 }; struct StatisticsType { float failRate; DateTypelastServiced;// DateType is a struct type int downDays; }; struct MachineRec { int idNumber; string description; StatisticsType history; // StatisticsType is a struct DateType purchaseDate; float cost; }; MachineRec machine; 4

5. 5 struct type variable machine 7000.idNumber.description. history.purchaseDate.cost.month.day.year 5719 “DRILLING…” 3 21 1995 8000.0.failrate.lastServiced.downdays.02 1 25 1999 4.month.day.year machine.history.lastServiced.year has value 1999

6. 6 Unions in C++ DEFINITION A union is a struct that holds only one of its members at a time during program execution. EXAMPLE union WeightType { long wtInOunces; int wtInPounds; Only one at a time float wtInTons; };

7. 7 Using Unions union WeightType // Declares a union type { long wtInOunces; int wtInPounds; float wtInTons; }; WeightType weight; // Declares a union variable weight.wtInTons = 4.83; // Weight in tons is no longer needed // Reuse the memory space weight.wtInPounds = 35; 7

8. 8 Abstraction l Abstraction is the separation of the essential qualities of an object from the details of how it works or is composed n Focuses on what, not how n Is necessary for managing large, complex software projects

9. 9 Control Abstraction l Constrol abstraction separates the logical properties of an action from its implementation Search (list, item, length, where, found); l The function call depends on the function’s specification (description), not its implementation (algorithm)

10. 10 Data Abstraction l Data abstraction separates the logical properties of a data type from its implementation LOGICAL PROPERTIESIMPLEMENTATION What are the possible values?How can this be done in C++? What operations will be needed?How can data types be used?

11. 11 Data Type set of values (domain) allowable operations on those values FOR EXAMPLE, data type int has domain -32768... 32767 operations +, -, *, /, %, >>, <<

12. 12 Abstract Data Type (ADT) l An abstract data type is a data type whose properties (domain and operations) are specified (what) independently of any particular implementation (how) For example...

13. 13 ADT Specification Example TYPE Time DOMAIN Each Time value is a time in hours, minutes, and seconds. OPERATIONS Set the time Print the time Increment by one second Compare 2 times for equality Determine if one time is “less than” another

14. 14 Another ADT Specification TYPE ComplexNumber DOMAIN Each value is an ordered pair of real numbers (a, b) representing a + bi OPERATIONS Initialize the complex number Write the complex number Add Subtract Multiply Divide Determine the absolute value of a complex number

15. 15 ADT Implementation l ADT implementation n Choose a specific data representation for the abstract data using data types that already exist (built-in or programmer-defined) n Write functions for each allowable operation

16. 16 10 45 27 Several Possible Representations of ADT Time 3 int variables 3 strings 3-element int array Choice of representation depends on time, space, and algorithms needed to implement operations 10 45 27 “10” “45” “27”

17. 17 Some Possible Representations of ADT ComplexNumber struct with 2 float members 2-element float array -16.2 5.8.real.imag

18. 18 C++ Data Types structured array struct union class address pointer reference simple integral enum char short int long bool floating float double long double

19. 19 class Time Specification // Specification file (Time.h) class Time // Declares a class data type {// does not allocate memory public : // Five public function members void Set (int hours, int mins, int secs); void Increment (); void Write () const; bool Equal (Time otherTime) const; bool LessThan (Time otherTime) const; private : // Three private data members int hrs; int mins; int secs; }; 19

20. 20 C++ classType l Facilitates re-use of C++ code for an ADT l Software that uses the class is called a client l Variables of the class type are called class objects or class instances l Client code uses class’s public member functions to manipulate class objects

21. 21 Client Code Using Time #include “time.h” // Includes specification of the class using namespace std; int main () { Time currentTime; // Declares two objects of Time Time endTime; bool done = false; currentTime.Set (5, 30, 0); endTime.Set (18, 30, 0); while (! done) {... currentTime.Increment (); if (currentTime.Equal (endTime)) done = true; }; } 21

22. 22 The End of Chapter 11 – Part 2