Homework - University of North Carolina Wilmington



Homework

Chapter 7

Name: ___SOLUTION_____

Ex 7.1 [14] Which of the following are valid declarations? Which instantiate an array object? Explain your answers.

int primes = {2, 3, 4, 5, 7, 11}; //Not valid array declaration

float elapsedTimes[] = {11.47, 12.04, 11.72, 13.88}; //Not valid array declaration; loss of precision, array is float and literals are by default double. To fix use the explicit float modifier on the literals, i.e 11.47 should be 11.47f b/c 11.47 is double by default.

int[ ] scores = int[30]; //Not valid, does not instantiate the int via new

int [ ] primes = new {2,3,5,7,11}; //Not valid, mix of implicit and explicit array declaration

int[ ] scores = new int[30]; //Valid

char grades[ ] = {‘a’,’b’,’c’,’d’,’f’}; //Valid

char[ ] grades new char[ ]; //Not valid, does not specify the size of the array in new

Ex 7.4 [16]Write an array declaration and any necessary supporting classes to represent the following statements:

a. students’ names for a class of 25 students

String names[] = new String[25];

b. students’ test grades for a class of 40 students

double grades[] = new double [40];

c. credit-card transactions that contain a transaction number, a merchant name, and a charge

public class CreditCardTrans

{

//data members

long transNumber;

String merchantName;

float charge;

//Constructor

public CreditCardTrans(long tn, String mn, float ch){ … }

…

}

CreditCardTrans cc[] = {new CreditCardTrans(11234,”StoreXY”,34.45), new CreditCardTrans(3423341,”StoreABC”, 123.43)};

d. students’ names for a class and homework grades for each student

final int NUMSTUDENTS = 10; //number of students

final int NUMGRADES = 8;//each student will have 8 grades

String name = new String[10]; //10 students names

float grades[][] = new float[NUMSTUDENTS][NUMGRADES];

//first index refers to the student; it can be cross-referenced with name via the index, e.g. student 2 (index 3) name[3] her grades can be accessed by grades[3][i]

e. for each employee of the L&L International Corp: the employee number, hire date, and the amount of the last five raises

//Class Employee contains the employee number, hire date, and the amount of raises as data members.

Employee emp[MAX] = new Employee[MAX] // this will call default constructor so all data that will be held in array must be explicitly added

Ex 7.6 [10] Write code that prints the values stored in an array called names backwards.

public void backwards( String names[] )

{

for( int i= names.length, i>0, name--) //decrement over names array

System.out.println(names[i]);

}

Ex 7.8 [10] Write a method called sumArray that accepts an array of floating point values and returns the sum of the values stored in the array.

public double sumArray( double a[] )

{

double sum;

for( int i=0, i ................
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