Problem 1 Short Answers Why use the reserved words new or delete? Why use dynamic memory allocation?

Transcription

1 Problem 1 Short Answers Why use the reserved words new or delete? Why use dynamic memory allocation? What is a pointer? What is a reference variable? When would you use pointers over reference variables? Why? What is a struct? What is a class? Why binary? Why hex? 1

2 Problem 2. What does this code do? Consider the following three functions: void myfunction1(int num, int *ptr) *ptr = num; num = 10; void myfunction2(int &num, int *ptr) ptr = &num; num = 10; void myfunction3(int *num, int *ptr) ptr = num; *num = 10; a) What is the output to the screen when the following code executes? int numberone = 1; int *apointer = &numberone; int numberfive = 5; myfunction1(numberfive, apointer); cout << *apointer << endl; cout << numberfive << endl; 2

3 b) What is the output to the screen when the following code executes? int numberone = 1; int *apointer = &numberone; int numberfive = 5; myfunction2(numberfive, apointer); cout << *apointer << endl; cout << numberfive << endl; c) What is the output to the screen when the following code executes? int numberone = 1; int * apointer = &numberone; int numberfive = 5; myfunction3(&numberfive, apointer); cout << *apointer << endl; cout << *numberfive << endl; 3

4 Problem 3. Debug this code Given the following code to increase the value of a variable: void Increment(int x) x ++ ; int main() int num1 = 5; cout << Before = << num1 << endl; Increment(num1); cout << After = << num1 << endl; The Increment function needs to increase the value of num1 in main, but currently the code prints out the same value for num1 after the call to Increment(num1). (a) Show how you would modify the code using pass by reference so that the value of num1 is increased after the call to Increment(num1) (you don't have to rewrite all the code, just rewrite the lines that need to change or the lines you want to add). (b) Show how you would modify the code using pass by pointer so that the value of num1 is changed after the call to Increment(num1) (you don't have to rewrite all the code, just rewrite the lines that need to change or the lines you want to add). 4

5 4. Pointers & Dynamic Memory a) Write a function named findtop that will find at most 10 students with 4.0 gpa to store in an array of pointers called Top, given an array of 100 students called CS101. Use this function header: void findtop(studenttype CS101[100], studenttype *Top[10]) b) Write a function to dynamically create an array of students and return a pointer to the array. The function should ask the user for input on the number of students to create the array and ask the user to input the name, gpa, sid, grade for each student object in the array. Assume each student in the array is of type studenttype given above. 5

6 Problem 5 structs & Classes struct name string first; string last; ; class Employee public: Employee(); name getname(); //returns ename double getrate() return hourlyrate; double gethours();//total hours worked for the week void setname(string fname, string lname);//sets ename void setrate(double erate) hourlyrate=erate; void sethours(double ehours[]); //takes as input the number of hours worked each day //of the week and stores them in the workedhours array double computepaycheck(); //computes the total amount paid per week void printpaycheck(); //prints out the total amount paid per week //example: //Tommy Trojan worked 40 hours this week at an hourly //rate of $12. The total paycheck for this week //is $ private: name ename; // holds employee s name double hourlyrate; // amount paid per hour worked double workedhours[5]; // holds the number of hours // worked each day of the week // Monday to Friday ; a) In the file employee.cpp write the functions for Employee class that are not defined: name getname(), gethours(), sethours(double ehours[]), setname(string fname, string lname), computepaycheck(), printpaycheck() 6

7 b) What will this code printout: int main() double Hours[5]=8, 7, 2, 5, 8; Employee *Tommy = new Employee(); Tommy->setName( Tommy, Trojan ); Tommy->setHours(Hours); Tommy->setRate(15.25); cout << Tommy->computePaycheck() << endl; Tommy->printPaycheck(); c) Write a function that gets the number of employees and then dynamically creates an array of Employee to hold exactly the number of employees. This function should ask the user to input the name of each employee to be stored in the array. 7