Fondamenti di C++ - Cay Horstmann 1

Transcription

1 Fondamenti di C++ - Cay Horstmann 1 Review Exercises R10.1 Line 2: Can't assign int to int* Line 4: Can't assign Employee* to Employee Line 6: Can't apply -> to object Line 7: Can't delete object Line 10: Explicit parameter of seconds_from must be an object, not a pointer Line 11: Can't delete object Line 14: Can't apply dot operator to pointer Line 16: Need parentheses (*t2).get_minutes() R10.3 a) You reach the object to which the pointer points b) It depends. The object may appear to be valid for some time, but it iscorrupted eventually c) The program dies with a segmentation or general protection fault d) It depends. There may appear to be an object at the random memory location,or the program may die. R10.5 The program prints The first two values are separate objects. Thus, raising the salary of onedoesn't affect the other. The second pair of values are pointers to a shared object. R10.7 The computation p[i] reaches the value that starts at address of p + i *sizeof(int) and is sizeof(int) bytes long. Since sizeof(int)!= sizeof(double),those values are just memory blocks consisting of some of the bytes of floating-pointdata. They are meaningless when considered as integers. R10.9 a) The second storage location in the array b) A pointer to that location c) The same as a) d) The fifth storage location in the array e) A pointer to the sixth storage location in the array f) 3

2 Fondamenti di C++ - Cay Horstmann 2 R10.11 You cannot return the array as the function result. Therefore, you must passin the array as a parameter: void minmax(double values[], double result[]) R10.13 a) A pointer set to 0 b) A pointer set to point to an array that contains a single 0 byte c) An array that contains a single 0 byte R10.15 Both functions append to an existing memory array instead of returning anew string that contains the concatenation. Generally, returning a new stringis more convenient, but it is impossible if you work with character arrays. The strcat function does not check whether it exceeds the target array'scapacity. The strncat function can be used instead, but it is cumbersometo compute the maximum number of characters to copy, and even more cumbersometo deal with the 0 terminator. The + operator simply allocates a string ofthe correct size. Programming Exercises P10.1 #include <string> #include <iomanip> #include <vector> using namespace std; class Person public: Constructs a person with a given n the name Person(string n); Gets the name of this the name string get_name() const; Sets the best friend of this p a pointer to the best friend void set_best_friend(person* p); Gets the best friend of this a pointer to the best friend

3 Fondamenti di C++ - Cay Horstmann 3 Person* get_best_friend() const; Adjusts the popularity counter of this d +1 or -1 void adjust_popularity(int d); Gets the popularity counter of this the popularity counter int get_popularity() const; private: string name; Person* best_friend; int popularity; ; Person::Person(string n) name = n; best_friend = NULL; popularity = 0; void Person::set_best_friend(Person* p) if (best_friend!= NULL) best_friend->adjust_popularity(-1); best_friend = p; if (best_friend!= NULL) best_friend->adjust_popularity(1); Person* Person::get_best_friend() const return best_friend; void Person::adjust_popularity(int d) popularity = popularity + d; int Person::get_popularity() const return popularity; string Person::get_name() const return name; vector<person*> people; bool more = true; while (more)

4 Fondamenti di C++ - Cay Horstmann 4 cout << "Enter name, q to quit: "; string name; getline(cin, name); if (name == "q") more = false; else people.push_back(new Person(name)); for (int i = 0; i < people.size(); i++) cout << "Who is the best friend of " << people[i]->get_name() << "? "; string name; getline(cin, name); for (int j = 0; j < people.size(); j++) if (people[j]->get_name() == name) people[i]->set_best_friend(people[j]); for (int i = 0; i < people.size(); i++) cout << setw(20) << people[i]->get_name() << "best friend=" << setw(20) << people[i]->get_best_friend()- >get_name() << "popularity=" << setw(10) << people[i]->get_popularity() << "\n"; P10.3 #include <string> #include <vector> class BankAccount public: Constructs a bank account with a zero balance. BankAccount(); Deposits money into this amount the amount to deposit. void deposit(double amount); Withdraws money from this amount the amount to withdraw. void withdraw(double amount); Gets the balance of this the balance double get_balance() const;

5 Fondamenti di C++ - Cay Horstmann 5 private: double balance; ; class Employee public: Constructs an employee with a given name, salary, and bank n the s the annual a a pointer to the bank account Employee(string n, double s, BankAccount* a); Deposits one month's salary into the bank account. void deposit_monthly_salary(); Prints this employee's information to cout. void print() const; private: string name; double salary; BankAccount* account; ; BankAccount::BankAccount() balance = 0; void BankAccount::deposit(double amount) balance = balance + amount; void BankAccount::withdraw(double amount) balance = balance - amount; double BankAccount::get_balance() const return balance; Employee::Employee(string n, double s, BankAccount* a) name = n; salary = s; account = a; void Employee::deposit_monthly_salary()

6 Fondamenti di C++ - Cay Horstmann 6 const int MONTHS_PER_YEAR = 12; account->deposit(salary / MONTHS_PER_YEAR); void Employee::print() const cout << "Employee[name=" << name << ",salary=" << salary << ",account balance=" << account->get_balance() << "]\n"; vector<employee> staff; bool more = true; string previous_lname = "q"; BankAccount* previous_account = NULL; while (more) string lname; cout << "Enter last name, q to quit: "; getline(cin, lname); if (lname == "q") more = false; else string fname; cout << "Enter first name: "; getline(cin, fname); cout << "Enter salary: "; double salary; cin >> salary; string dummy; getline(cin, dummy); if (lname!= previous_lname) previous_account = new BankAccount(); previous_lname = lname; staff.push_back(employee(lname + ", " + fname, salary, previous_account)); for (int i = 0; i < staff.size(); i++) staff[i].deposit_monthly_salary(); for (int i = 0; i < staff.size(); i++) staff[i].print(); P10.5 Computes the average of the values in an a the array

7 Fondamenti di C++ - Cay Horstmann a_size the number of elements in the the average, or 0 if the array is empty double average(double a[], int a_size) double sum = 0; double* p = a; for (int i = 0; i < a_size; i++) sum = sum + *p; p++; if (a_size == 0) else return sum / a_size; double data[] = 1, 4, 9, 16, 25 ; cout << average(data, 5) << "\n"; P10.7 Reverses the values in an a the array void reverse(double a[], int a_size) double* p = a; double* q = a + a_size - 1; while (p < q) double temp = *p; *p = *q; *q = temp; p++; q--; double data[] = 1, 4, 9, 16, 25 ; reverse(data, 5); for (int i = 0; i < 5; i++) cout << data[i] << "\n"; P10.9

8 Fondamenti di C++ - Cay Horstmann 8 Computes the length of the prefix of a string that is composed of characters in a given s the string whose maximum prefix is to be t the string whose characters are to be contained in the the length of the prefix of s consisting of characters of t (in any order) int strspn(const char s[], const char t[]) int n = 0; while (*s!= '\0') const char* p = t; while (*p!= *s && *p!= '\0') p++; if (*p == 0) // no match return n; n++; s++; return n; cout << strspn("mississippi", "ims") << "\n"; P10.11 #include <cstring> Concatenates two character arrays into a result a the first character b the second character result the array to hold the result_maxlength the maximum length of the result (not counting the '\0' terminator) void concat(const char a[], const char b[], char result[], int result_maxlength) int n = strlen(a); strncpy(result, a, result_maxlength); if (n < result_maxlength) strncat(result + n, b, result_maxlength - n); result[result_maxlength] = '\0'; char a[] = "Woozle"; char b[] = "Heffalump"; char c[5];

9 Fondamenti di C++ - Cay Horstmann 9 char d[10]; char e[20]; concat(a, b, c, 5); concat(a, b, d, 10); concat(a, b, e, 20); cout << c << "\n"; cout << d << "\n"; cout << e << "\n"; P10.13 using namespace std; const int BUFFER_CAPACITY = 1000; const int LINES_CAPACITY = 100; char buffer[buffer_capacity]; char* lines[lines_capacity]; int buffer_size = 0; int lines_size = 0; bool more = true; bool newline = true; while (more) char c = cin.get(); if (cin.fail()) more = false; else if (buffer_size >= BUFFER_CAPACITY) more = false; if (newline) if (lines_size < LINES_CAPACITY) lines[lines_size] = buffer + buffer_size; lines_size++; newline = false; else more = false; if (more) if (c == '\n') buffer[buffer_size] = '\0'; buffer_size++; newline = true; else buffer[buffer_size] = c; buffer_size++;

10 Fondamenti di C++ - Cay Horstmann 10 buffer[buffer_capacity - 1] = '\0'; for (int i = lines_size - 1; i >= 0; i--) cout << lines[i] << "\n"; P10.15 using namespace std; int buffer_capacity = 1000; int lines_capacity = 100; char* buffer = new char[buffer_capacity]; char** lines = new char*[lines_capacity]; int buffer_size = 0; int lines_size = 0; bool more = true; bool newline = true; while (more) char c = cin.get(); if (cin.fail()) more = false; else if (buffer_size >= buffer_capacity) char* new_buffer = new char[2 * buffer_capacity]; for (int i = 0; i < buffer_capacity; i++) new_buffer[i] = buffer[i]; for (int i = 0; i < lines_size; i++) lines[i] = new_buffer + (lines[i] - buffer); buffer = new_buffer; buffer_capacity = 2 * buffer_capacity; if (newline) if (lines_size >= lines_capacity) char** new_lines = new char*[2 * lines_capacity]; for (int i = 0; i < lines_capacity; i++) new_lines[i] = lines[i]; lines = new_lines; lines_capacity = 2 * lines_capacity; lines[lines_size] = buffer + buffer_size; lines_size++; newline = false; if (c == '\n') buffer[buffer_size] = '\0';

11 Fondamenti di C++ - Cay Horstmann 11 buffer_size++; newline = true; else buffer[buffer_size] = c; buffer_size++; for (int i = lines_size - 1; i >= 0; i--) cout << lines[i] << "\n";