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User-Defined Classes Chapter 10. 2 10.1 Class Definition t int, float, char are built into C+ t Declare and use –int x = 5; t Create user defined data.

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Presentation on theme: "User-Defined Classes Chapter 10. 2 10.1 Class Definition t int, float, char are built into C+ t Declare and use –int x = 5; t Create user defined data."— Presentation transcript:

1 User-Defined Classes Chapter 10

2 2 10.1 Class Definition t int, float, char are built into C+ t Declare and use –int x = 5; t Create user defined data types –Extensive use throughout remainder of course t Counter class will introduce the concept –counter.h counter class definitions –Define the class in the.h file

3 3 User Defined Types t Define what data we want in the class –data elements of the class are private t Create the functionality to operate on the data –class member functions access data t We have created a new data type not known to the compiler

4 4 Counter.h // FILE: Counter.h // COUNTER CLASS DEFINITION #ifndef COUNTER_H #define COUNTER_H class counter { public: counter (); counter (int);

5 5 Counter.h // SET COUNTER VALUE void setCount (int); // INCREMENT COUNTER void increment (); // DECREMENT COUNTER void decrement (); // RETURN CURRENT COUNTER VALUE int getCount () const;

6 6 Counter.h // RETURN MAXIMUM COUNTER VALUE int getMaxValue () const; private: // Data Members (Attributes)... int count; int maxValue; }; #endif

7 7 Compiler Directives t Prevent multiple definitions #ifndefCOUNTER_H #define COUNTER_H #endif t 1st the #ifndef tests to see if COUNTER_H has been defined –If not the 2nd line #define defines the content –If defined skips to the #endif

8 8 Using the counter Class t Driver program CounterTest.cpp will help us see how the Counter Class is used t Must #include “Counter.h” because our class definitions are contained in it. –Change this view based on our compiler –#include “Counter.cpp”

9 9 CounterTest.cpp // File: CounterTest.cpp // Test the counter class #include #include "counter.h" #include "counter.cpp" using namespace std; int main() {

10 10 CounterTest.cpp counter c1; counter c2(10); // Test setValue, increment, decrement, and // accessValue functions. c1.setCount(50); c1.decrement(); c1.increment(); cout << "Final value of c1 is " << c1.getCount() << endl;

11 11 CounterTest.cpp c2.increment(); c2.decrement(); cout << "Final value of c2 is " << c2.getCount() << endl; return 0; }

12 12 10.2 Class Implementation t Counter.cpp implementation details t Hidden from users (details) t Scope resolution operator –:: prefix for each member function –Informs the compiler that the function is a member of the class t Class member functions can access all class data members –Avoid using member functions inside member functions

13 13 Constructors t Two special member functions –Same name as class name t Constructor executes each time an object of type counter is declared –counter mike; t Initializes object t Types –Default –Class

14 14 Constructors t Default Constructor –Used when no arguments passed as part of the declaration t Class Constructor –Used when arguments are passed as part of the declaration t Constructors do NOT specify a return type

15 15 Member Functions t Member functions that modify data are –setValue –increment –decrement t Member functions that retrieve data are –getvalue –getmaxvalue t Const; at the end of the function means no data changes by the function

16 16 Counter.cpp // File: counter.cpp // Counter class implementation #include "counter.h" #include using namespace std; // Default constructor counter::counter() { count = 0; maxValue = INTMAX; }

17 17 Counter.cpp // Constructor with argument counter::counter(int mVal) { count = 0; maxValue = mVal; } // Increment counter void counter::increment() { if (count < maxValue) count++;

18 18 Counter.cpp else cerr << "Counter overflow. Increment ignored." << endl; } // Decrement counter void counter::decrement() { if (count > 0) count--; else cerr << "Counter underflow. Decrement ignored." << endl; }

19 19 Counter.cpp // Set counter value void counter::setCount(int val) { if (val >= 0 && val <= maxValue) count = val; else cerr << "New value is out of range. Value not changed." << endl; } // Set maximum counter value void counter::setMaxValue(int val) {

20 20 Counter.cpp if (val >= 0 && val <= INTMAX) maxValue = val; else cerr << "New maxValue is out of range -- not changed." << endl; } // Return current counter value int counter::getCount() const { return count; }

21 21 Counter.cpp // Return maximum counter value int counter::getMaxValue() const { return maxValue; }

22 22 10.3 Summary of Rules for Use of Classes and Objects t Class Instance –counter c1; –Creates an instance of the counter class (object) –Default constructor invoked –Allocates space in memory for object t Similar to other data type declarations –int value; –Space in memory allocated for a data type int

23 23 Private vs Public t Public member functions allow users to operate on the counter object c1 t May have private member functions –If member functions need to call another function not part of the class it should be private t Use care when defining public access t Users of a class are clients t Class sometimes referred to as the server

24 24 Syntax Form: class className { public: List all public data and functions private: List all private data and functions };

25 25 Comparing struct and classes t struct & class define a data type –Collection of related elements –Prototype declarations –Three levels of access control –Public –Private –Protected (not covered) t Major difference default access opposite –class private - struct public

26 26 Function Overloading & Polymorphism t Functions with the same name is called function overloading t Polymorphism is what allows functions with the same name to do different things based on its arguments

27 27 10.4 Classes as Operands and Arguments t Assignment operator can be used t Others must be re-defined (Chap 11) –Operator Overloading t Use C& ob1 as formal reference argument t Use const C& ob1 to specify object can’t be modified by a function –Efficiency issues

28 28 CompareCounter c1.compareCounter (c2) ; or c2.compareCounter (c1); int counter::compareCounter (const counter& aCounter) const { int result; if (count <= aCounter.count) result = -1; else if (count == aCounter.count) result = 0; else result = 1; return result; }

29 29 10.5 A Fraction Class t Design of Fraction Class –Data represents Numerator –Data represents Denominator t FractionTest.cpp t Fraction.cpp

30 30 FractionTest.cpp // File: fractiontest.cpp // Tests the fraction class. #include #include "fraction.h" #include "fraction.cpp" using namespace std; int main() { fraction f1, f2; fraction f3;

31 31 FractionTest.cpp // Read two fractions cout << "Enter 1st fraction: " << endl; f1.readFrac(); cout << "Enter 2nd fraction: " << endl; f2.readFrac(); if (f1 == f2) cout << "same" << endl; // Display results of fraction arithmetic f3 = f1.multiply(f2); f1.displayFrac(); cout << " * "; f2.displayFrac(); cout << " = ";

32 32 FractionTest.cpp f3.displayFrac(); cout << endl; f3 = f1.divide(f2); f1.displayFrac(); cout << " / "; f2.displayFrac(); cout << " = "; f3.displayFrac(); cout << endl; //f3 = f1.add(f2); f3 = f1 + f2; f1.displayFrac(); cout << " + "; f2.displayFrac(); cout << " = "; f3.displayFrac(); cout << endl;

33 33 FractionTest.cpp f3 = f1.subtract(f2); f1.displayFrac(); cout << " - "; f2.displayFrac(); cout << " = "; f3.displayFrac(); cout << endl; return 0; }

34 34 Fraction.cpp // File: Fraction.cpp // Fraction class implementation #include "fraction.h" #include using namespace std;

35 35 Fraction.cpp // Member functions // Constructors fraction::fraction() { num = 0; denom = 1; } fraction::fraction(int n) { num = n; denom = 1; }

36 36 Fraction.cpp fraction::fraction(int n, int d) { num = n; denom = d; } // Set numerator and denominator void fraction::setNum(int n) { num = n; }

37 37 Fraction.cpp void fraction::setDenom(int d) { denom = d; } // Multiply fractions fraction fraction::multiply(const fraction& f) { fraction temp(num * f.num, denom * f.denom); return temp; }

38 38 Fraction.cpp // Divide fractions fraction fraction::divide(const fraction& f) { fraction temp(num * f.denom, denom * f.num); return temp; } // Add fractions fraction fraction::add(const fraction& f) { fraction temp(num * f.denom + f.num * denom, denom * f.denom); return temp; }

39 39 Fraction.cpp // Subtract Fractions fraction fraction::subtract(const fraction& f) { fraction temp(num * f.denom - f.num * denom, denom * f.denom); return temp; }

40 40 Fraction.cpp // Read a fraction void fraction::readFrac() { char slash; // storage for / do { cout << "Enter numerator / denominator: "; cin >> num >> slash >> denom; } while (slash != '/'); }

41 41 Fraction.cpp // Display a fraction void fraction::displayFrac() const { cout << num << '/' << denom; } // Accessors int fraction::getNum() const { return num; }

42 42 Fraction.cpp fraction fraction::operator + (const fraction& f2) // IN: right-operand { fraction temp(num * f2.denom + f2.num * denom, denom * f2.denom); return temp; } bool fraction::operator == (const fraction& f) { return(num == f.num && denom == f.denom); }

43 43 Fraction.cpp int fraction::getDenom() const { return denom; }

44 44 10.6 Circle Class t Data members to represent x & y coordinates t Radius t Color t Area t Perimeter t See specification on page 509

45 45 Circle.h // File circle.h // Circle class definition #ifndef CIRCLE_H #define CIRCLE_H class circle { public: // enumeration type enum color {black, blue, green, cyan, red, magenta, brown, lightgray, nocolor};

46 46 Circle.h // Member Functions // constructor circle(); // Set center coordinates void setCoord(int, int); // Set radius void setRadius(float); // Set color void setColor(color);

47 47 Circle.h // Compute the area void computeArea(); // Compute the perimeter void computePerimeter(); // Display attributes void displayCircle() const;

48 48 Circle.h // accessor functions int getX() const; int getY() const; float getRadius() const; color getColor() const; float getArea() const; float getPerimeter() const;

49 49 Circle.h private: // Data members (attributes) int x; int y; float radius; color cColor; float area; float perimeter; }; #endif // CIRCLE_H

50 50 CircleTest.cpp // File circletest.cpp // Tests the Circle class #include "circle.h" #include "circle.cpp" #include using namespace std; int main() {

51 51 CircleTest.cpp circle myCircle; // Set circle attributes. myCircle.setCoord(150, 100); myCircle.setRadius(10); myCircle.setColor(circle::magenta); // Compute area and perimeter myCircle.computeArea(); myCircle.computePerimeter();

52 52 CircleTest.cpp // Display the circle attributes. cout << "The circle attributes follow:" << endl; myCircle.displayCircle(); return 0; }

53 53 CircleTest.cpp Program Output The circle attributes follow: x-coordinate is 150 y-coordinate is 100 radius is 10 color is 5 area is 314.159 perimeter is 62.8318

54 54 Circle.cpp // File circle.cpp // Circle class implementation #include "circle.h" #include using namespace std; const float PI = 3.14159;

55 55 Circle.cpp // Member Functions... // constructor circle::circle() { x = 0; y = 0; radius = 0; cColor = nocolor; area = 0.0; perimeter = 0.0; }

56 56 Circle.cpp // Set center position void circle::setCoord(int xx, int yy) { x = xx; y = yy; } // Set radius void circle::setRadius(float r) { radius = r; computeArea(); computePerimeter(); }

57 57 Circle.cpp // Set color void circle::setColor(color c) { cColor = c; } // Compute the area void circle::computeArea() { area = PI * radius * radius; }

58 58 Circle.cpp // Compute the perimeter void circle::computePerimeter() { perimeter = 2 * PI * radius; } // Display attributes void circle::displayCircle() const { cout << "x-coordinate is " << x << endl; cout << "y-coordinate is " << y << endl; cout << "color is " << int(cColor) << endl;

59 59 Circle.cpp cout << "area is " << area << endl; cout << "perimeter is " << perimeter << endl; } // accessor functions circle::color circle::getColor() const { return cColor; } // Insert definitions for rest of accessor functions here. //...

60 60 Circle.cpp int circle::getX() const { return x; } int circle::getY() const { return y; } float circle::getRadius() const { return radius; }

61 61 Circle.cpp float circle::getArea() const { return area; } float circle::getPerimeter() const { return perimeter; }

62 62 10.7 A Simple String Class t Since we have a string class we might take it for granted t What do we need in a string class ? –create a string –length –capacity –at –read & write t Look at SimpleString.h

63 63 SimpleString.h // File simpleString.h // Simple string class definition #ifndef SIMPLESTRING_H #define SIMPLESTRING_H class simpleString { public: // Member Functions // constructor simpleString();

64 64 SimpleString.h // Read a simple string void readString(); // Display a simple string void writeString() const; // Retrieve the character at a specified // position // Returns the character \0 if position is // out of bounds char at(int) const;

65 65 SimpleString.h // Return the string length int getLength() const; // Return the string capacity int getCapacity() const; void getContents(char[]) const;

66 66 SimpleString.h private: // Data members (attributes) enum {capacity = 255}; char contents[capacity]; int length; }; #endif //SIMPLESTRING_H

67 67 SimpleStringTest.cpp // File: simpleStringTest.cpp // Tests the simple string class #include "simpleString.h" #include "simpleString.cpp" #include using namespace std; int main() {

68 68 SimpleStringTest.cpp simpleString aString; // input - data string // Read in a string. cout << "Enter a string and press RETURN: "; aString.readString(); // Display the string just read. cout << "The string read was: "; aString.writeString(); cout << endl;

69 69 SimpleStringTest.cpp // Display each character on a separate line. cout << "The characters in the string follow:" << endl; for (int pos = 0; pos < aString.getLength(); pos++) cout << aString.at(pos) << endl; return 0; }

70 70 SimpleStringTest.cpp Program Output Enter a string and press RETURN: Philly cheesesteak The string read was: Philly cheesesteak The characters in the string follow: P h i.etc etc a k

71 71 SimpleString.cpp // File simplestring.cpp // Simple string class implementation #include "simplestring.h" #include using namespace std; // Member Functions... // constructor simpleString::simpleString() { length = 0; // Denotes an empty string }

72 72 SimpleString.cpp // Read a simple string void simpleString::readString() { // Local data... char next; int pos = 0; cin.get(next); while ((next != '\n') && (pos < capacity)) {

73 73 SimpleString.cpp // Insert next in array contents contents[pos] = next; pos++; cin.get(next); } length = pos; }

74 74 SimpleString.cpp // Write a simple string void simpleString::writeString() const { for (int pos = 0; pos < length; pos++) cout << contents[pos]; } // Retrieve the character at a specified position // Returns the character \0 if position is out // of bounds char simpleString::at(int pos) const { // Local data const char nullcharacter = '\0';

75 75 SimpleString.cpp if ((pos = length)) { cerr << "Character at position " << pos << " not defined." << endl; return nullcharacter; } else return contents[pos]; }

76 76 SimpleString.cpp // Return the string length int simpleString::getLength() const { return length; } // Return the string capacity int simpleString::getCapacity() const { return capacity; }

77 77 SimpleString.cpp void simpleString::getContents(char str[]) const { for (int i = 0; i < length; i++) str[i] = contents[i]; }

78 78 10.8 A Savings Account Class t Problem Statement (see page 522) t Analysis t Design t Implementation t Test & Verification

79 79 Savings.h // File Savings.h // Savings account class definition #include "money.h" // access money class #include // access string class using namespace std; #ifndef SAVINGS_H #define SAVINGS_H

80 80 Savings.h class savings { public: // Member Functions... // constructor savings(); // Open a new account void openAccount(); // Change account name void changeName(int, string);

81 81 Savings.h // Add quarterly interest void addInterest(); // Process a deposit void deposit(int, money); // Process a withdrawal void withdraw(int, money); // Close an account void closeAccount(int);

82 82 Savings.h // Get account balance money getBalance() const; private: // Data members (attributes) int id; string name; money balance; float interestRate;

83 83 Savings.h // Member functions... // Validate user identification bool validId(int) const; }; #endif // SAVINGS_H

84 84 Savings.cpp // File savings.cpp // Savings account implementation file #include "savings.h" #include "money.h" #include using namespace std;

85 85 Savings.cpp // Member Functions... // constructor savings::savings() { name = ""; id = 0; balance = 0.0; interestRate = 0.0; }

86 86 Savings.cpp // Open a new account void savings::openAccount() { cout << "Account name: "; getline(cin, name, '\n'); cout << "Account ID: "; cin >> id; cout << "Initial balance: $"; cin >> balance; cout << "Annual interest rate percentage: %"; cin >> interestRate; }

87 87 Savings.cpp // Validate user id bool savings::validId(int ident) const { if (id == ident) return true; else { cerr << "Error - ID's do not match! "; return false; }

88 88 Savings.cpp // Change account name void savings::changeName(int ident, string na) { if (validId(ident)) { name = na; cout << "Changing account name to " << na << endl; } else cerr << "Reject name change request." << endl; }

89 89 Savings.cpp // Add quarterly interest void savings::addInterest() { // Local data float quarterRateFrac; quarterRateFrac = interestRate / 400.0; balance += balance * quarterRateFrac; }

90 90 Savings.cpp // Process a deposit void savings::deposit(int ident, money amount) { if (validId(ident)) { balance += amount; cout << "Depositing " << amount << endl; } else cerr << "Reject deposit of " << amount << endl; }

91 91 Savings.cpp // Process a withdrawal void savings::withdraw(int ident, money amount) { if ((validId (ident)) && (amount <= balance)) { balance -= amount; cout << "Withdrawing " << amount << endl; } else cerr << "Reject withdrawal of " << amount << endl; }

92 92 Savings.cpp // Close an account void savings::closeAccount(int ident) { if (validId(ident)) { cout << "Final balance for account number " << id << " is " << balance << endl; cout << "Account has been closed" << endl; balance = 0.0; id = 0; name = ""; }

93 93 Savings.cpp else cerr << "Account not closed" << endl; } // Get account balance money savings::getBalance() const { return balance; }

94 94 Testing the Class t Use a driver to test –SavingsTest.cpp t Create savings objects t Operates on the declared objects t Try valid and invalid data

95 95 SavingsTest.cpp // File savingsTest.cpp // Tests the savings class #include #include "savings.h" #include "savings.cpp" #include "money.h" #include "money.cpp" using namespace std;

96 96 SavingsTest.cpp int main() { savings myAccount; // Open a savings account. myAccount.openAccount(); cout << endl; // Make valid and invalid deposit. myAccount.deposit(1234, 500.00); myAccount.deposit(1111, 300.00);

97 97 SavingsTest.cpp // Get and display balance. cout << endl << "Current balance is " << myAccount.getBalance() << endl; // Make valid and invalid withdrawal. myAccount.withdraw(1234, 750.00); myAccount.withdraw(1234, 15000.00); // Add interest. myAccount.addInterest();

98 98 SavingsTest.cpp // Close the account. myAccount.closeAccount(1234); return 0; }

99 99 SavingsTest.cpp Program Output Account name: William Gates Account ID: 1234 Initial Balance: $1000.00 Annual interest rate percentage: %5 Depositing $500.00 Error - Ids do not match ! Reject deposit of $300.00 Current balance is $1,500.00 Withdrawing $750.00 Reject withdrawal of $15,000.00 Final balance for account number 1234 is $759.38 Account has been closed

100 100 10.9 Common Programming Errors t Function argument & return value errors t Not defining a function as a member of a class t Prefixing a class function call –obj.function(); t Referencing a private attribute of a class t Missing header files t Missing ; on class definition

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