CS 31 Discussion: Final Week. Taylor Caulfield

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1 CS 31 Discussion: Final Week Taylor Caulfield

2 Overview for this Week Review Practice Problems

3 Review Topics to Study Control Flow (if/switch branch, for/while/do-while loop) Functions/Parameters Arrays C-Strings Structs/Classes Pointers Constructors/Destructors

4 Constructors Constructor: a function that is invoked when an instance of a class is created called immediately upon object creation can take parameters multiple constructors for a class can exist, as long as each one has different parameters You can create a new variable for a pointer variable to point to by assigning the pointer variable the value "new ClassConstructor" ClassConstructor is any constructor for the class space will be allocated for the new variable and the variable's address will be assigned to scp Destructor: a function that is invoked when an instance of a class is bound for deletion (whether by the delete statement or by going out of scope) good for releasing held resources or doing maintenance before destruction destructor is invoked before the actual deletion of the object cannot take parameters (so only one destructor per class) is NOT automatically called when exit() is used be careful if you are using destructors for maintenance work

5 Constructors More Constructors/Destructors specifics Must have the same name as their class Cannot be explicitly called Does not have a return type SomeClass sc = SomeClass(50); //Call the constructor for a variable SomeClass * scp = new SomeClass(50); //Create a new variable that this pointer will point to delete sc; //the destructor for scp is called before deletion

6 Problem 1 Remove the invalid Constructors/Destructors class SomeClass public: SomeClass(); SomeClass(int x); SomeClass(int x, int y); SomeClass(int y, int z); SomeClass(int y, char z); ~SomeClass(); ~SomeClass(int x);

7 Problem 2 int something(int * &x, int val) *x += val; return *x++; int main() int arr_matey[5] = 7,3,8,1,5 ; int *parr = arr_matey + 1; int y = something(parr, 10); int *parr2 = &arr_matey[y % 5]; int z = something(parr2, *(parr + (y % 4))); Show or describe the output of the following statements after the above code is run. If a statement produces undefined output or results in an error, explain why. cout << arr_matey; cout << parr[0]; cout << y; cout << z;

8 Problem 3 char e[10] = "edfghk"; char *f = e; Which of the following statements will assign the value of e's second element to its seventh element? e[6] = *f++; e[6] = *++f; f[6] = *f++; f[6] = *++f; f++[5] = *++f; strcat(e,*(f+1)); strcpy(f+4,e++); strcpy(f+4,e);

9 Problem 4 What lucky number(s) from 0-10 will nab you an 'A' for your letter grade? What lucky number(s) from 0-10 will cause the loop to run exactly 3 times? void get_final_grade(int &o_score, char &o_grade, int &lucky_number) int times = 0; do o_score = (o_score + lucky_number * 7) % 100; o_grade = 'J' - o_score / 10; lucky_number -= o_score / 10; times++; cout << "I have been grading for " << times << " hours." << endl; while (lucky_number > 0); int overall_score = 93; char overall_grade = 'F'; int my_lucky_number =? get_final_grade(overall_score, overall_grade, my_lucky_number); cout << "Your final grade for this class is: " << overall_grade << endl;

10 Problem 5 char winner[20] = "The winner is: "; int x = 155;?? cout << winner; Replace?? with code that will make winner display "The winner is: x" (x being whatever value is contained in the integer x) Make sure that no buffer overflows can occur.

11 Problem 6A #include <iostream> #include <string> #include <random> #include <utility> #include <cstdlib> using namespace std; const int MAX_ROBOTS = 50; const int HOME_COUNT = 5; class Home public: Home(int x, int y); int getx() const; int gety() const; private: int m_x; int m_y; ; class Robot public: Robot(Home* hm, int x, int y); private: int int Home* ; int getx() const; int gety() const; void move(int n_x, int n_y); void gohome(); m_x; m_y; m_home; class World public: World(int m_x, int m_y); ~World(); Home * gethome(int h_ind); int gettotalrobots() const; int getrobotsat(int h_ind) const; void addrobot(int h_ind); void moverobot(int r_ind, int n_x, int n_y); void sendrobothome(int r_ind); void annihilaterobots(int h_ind); private: int max_x; int max_y; int n_robots; Robot* m_robots[max_robots]; Home* m_homes[home_count]; ; int randint(int min, int max) if (max < min) swap(max, min); static random_device rd; static mt19937 generator(rd()); uniform_int_distribution<> distro(min, max); return distro(generator);

12 Problem 6A Robot Constructor initializes the robot's home and current coordinates move(int n_x, int n_y) makes the robot move n_x spaces horizontally and n_y spaces vertically from its current position gohome() makes the robot go to the coordinates of its home Home Constructor initializes the home's coordinates World Constructor defines the world's dimensions (given by max_x and max_y), and creates HOUSE_COUNT homes within those dimensions Destructor destroys all robots and all homes gethome(int h_ind) returns the home at index h_ind gettotalrobots() returns the number of robots currently in existence getrobotsat(int h_ind) returns the number of existing robots currently at the specified home addrobot(int h_ind) adds a robot whose home is the home with index h_ind, and initializes it position to be random moverobot(int r_ind, int n_x, int n_y) has the robot at index r_ind call move(n_x,n_y) sendrobothome(int r_ind) sends the specified robot to its home annihilaterobots() destroys all robots at the specified home randint(int min,int max) returns a random number between min and max

13 Problem 6A Spot the errors in the Home and Robot functions Home(World* wd, int x, int y) m_x = x; m_y = y; int Home::getx() const return m_x; int Home::gety() const return m_y; Robot(Home* hm, int x, int y) m_x = x; m_y = y; int Robot::getx() const return m_x; int Robot::gety() const return m_y; int Robot::move(int n_x, int n_y) m_x += n_x; m_y += n_y; int Robot::goHome() m_x = hm.m_x; m_y = hm.m_y;

14 Problem 6B Write the constructor for the World class. The constructor defines the world's dimensions (given by max_x and max_y), and creates HOUSE_COUNT homes within those dimensions. A world starts off with 0 robots.

15 Problem 6C Spot the errors in these World functions. If a statement may access a null pointer, explain how to prevent it from doing so. Home * World::getHome(int h_ind) return m_homes[h_ind]; int World::getTotalRobots() const return n_robots; int World::getRobotsAt(h_ind) const int tally = 0; for (int i = 0; i < MAX_ROBOTS; i++) if (m_robots[n_robots]->m_x == m_homes[i].getx && m_robots[n_robots]->m_y == m_homes[i].gety) tally ++; return tally; void World::addRobot(int h_ind) m_robots[n_robots] = new Robot(m_homes[h_ind],randInt(0,max_x),randInt(0,max_y)); void World::moveRobot(int r_ind, int n_x, int n_y) m_robots[r_ind]->move(n_x,n_y); void World::sendRobotHome(int r_ind) m_robots[r_ind]->gohome();

16 Problem 6D Write the annihilate_robots function of the World class. A destroyed robot is deleted (their memory should be deallocated) void annihilate_robots(int t_ind)...

17 Problem 6E Write the destructor for the World class. All homes and all robots in existence should be deleted.

18 Problem 6F Using annihilate_robots only once, replace?? with a code segment that destroys exactly 7 robots. int main() World wd = World(500,500); for (int i = 0; i < 35; i++) wd.addrobot(i % HOME_COUNT); cout << wd.gettotalrobots() << endl;?? cout << wd.gettotalrobots() << endl;