6.096 Introduction to C++

Transcription

1 MIT OpenCourseWare Introduction to C++ January (IAP) 2009 For information about citing these materials or our Terms of Use, visit:

2 MASSACHUSETTS I STITUTE OF TECH OLOGY 6.096: Introduction to C++ IAP 2009 PROBLEM SET 6 SOLUTIO S Problem 1 (a) #include <ctime> class Time time_t t; ; // or long, or int Time( long initialtime = time(0) ) t = initialtime; long gettime() return t; ; void settime(long newtime) t = newtime; ; (b) #include <ctime> class Time time_t t; // or long, or int Time(time_t initialtime = time(0) ) : t(initialtime) int gettime() return t; void settime(time_t newtime) t= newtime;

3 ; Problem 2 #include <iostream> using namespace std; class Complex double real, imaginary; Complex(double realpart=0, double imagpart=0) real=realpart; imaginary=imagpart;; double getreal() return real; ; double getimaginary() return imaginary; ; void set(double realpart, double imagpart) real = realpart; imaginary = imagpart; ; Complex add(const Complex &obj) const return Complex(real + obj.real, imaginary + obj.imaginary ); ; Complex subtract(const Complex &obj) const return Complex(real - obj.real, imaginary - obj.imaginary ); ; Complex multiply(const Complex &obj) const return Complex(real * obj.real -imaginary * obj.imaginary, real * obj.imaginary + imaginary * obj.real); ; ; Problem 3 (UNGRADED) Error 1: The first occurs in function getincrementeddata. The function is declared const, but it modifies the object.

4 Correction: To correct the first error, remove the const keyword from the definition of getincrementeddata. Error 2: The second error occurs in function getcount. This function is declared static, so it is not allowed to access any non-static member of the class. Correction: To correct the second error, remove the output line from the getcount definition. Problem 4 1. A base class s protected members can be accessed only in the base-class definition or in derived-class definitions. 2. A base class s public members are accessible within that base class and anywhere that the program has a handle to an object of that base class or to an object of one of its derived classes. 3. A base class s protected access members have a level of protection between those of public and private access. 4. When deriving a class from a base class with public inheritance, public members of the base class become public members of the derived class, and protected members of the base class become protected members of the derived class. 5. When deriving a class from a base class with protected inheritance, public members of the base class become protected members of the derived class, and protected members of the base class become protected members of the derived class. Problem 5 #include <iostream> #include <cmath> using namespace std; class Account //part A double balance; Account(double initbalance); void Credit(double amounttocredit); bool Debit(double amounttodebit); double getbalance(); ;

5 Account::Account(double initbalance):balance(initbalance) if(balance<0.0) balance=0.0; cerr << "Invalid balance, must be non-negative"<<endl// or cout << "Setting balance to zero"<<endl; double Account::Credit(double amounttocredit) balance += amounttocredit; return balance; bool Account::Debit(double amounttodebit) if(balance >= amounttodebit) balance -= amounttodebit; return true; else cerr << "Debit amount exceeded account balance."<<endl; return false; double Account::getBalance() return balance; class SavingsAccount: public Account //part B double interestrate; SavingsAccount(double interestrate, double initbalance); double calculateinterest(int years); ;

6 SavingsAccount::SavingsAccount(double interestrate, double initbalance) : Account(initBalance) interestrate=interestrate; double SavingsAccount::calculateInterest(int years) return balance * pow(1+interestrate, years); class CheckingAccount: public Account //part C double fee; CheckingAccount(double transactionfee, double initbalance); void Credit(double amounttocredit); bool Debit(double amounttodebit); ; CheckingAccount::CheckingAccount(double transactionfee, double initbalance) : Account(initBalance) fee = transactionfee; void CheckingAccount::Credit(double amounttocredit) Account::Credit( amounttocredit -fee ); bool CheckingAccount::Debit(double amounttodebit) return Account::Debit(amountToDebit + fee); Problem 6 Array.h #include <iostream> #include <string> using namespace std;

7 class Array const int size; int *internalarray; Array(int numelements); Array(int[] initialvalues, int numelements); Array(const Array &); int getlength() return size; int &getelement(const int); const int &getelement(const int) const; void print(const string &separator); ~Array(); ; Array.cpp #include <iostream> #include <string> #include "Array.h" using namespace std; Array::Array(int numelements) : size(numelements) internalarray = new int[size]; for(int i = 0; i < size; i++) internalarray[i] = 0; Array::Array(int initialvalues[], int numelements) : size(numelements) internalarray = new int[size]; for(int i = 0; i < size; i++) internalarray[i] = initialvalues[i]; Array::Array(const Array &a) : size( a.getlength() ) internalarray = new int[size]; for(int i = 0; i < size; i++) internalarray[i] = a.internalarray [i]; int &Array::getElement(const int n) return internalarray[n]; const int &Array::getElement(int n) const

8 return internalarray[n]; void Array::print(const string &separator) cout << internalarray[0]; for(int i=1; i<size; i++) cout << separator << internalarray[i]; Array::~Array() delete[] internalarray; ;