Cpcs 203 -array-problems

CPCS 203 Lab sheet 1
Student Name:_____________________________ Section:__

King Abdulaziz University
Faculty of Computing and Information Systems
Spring Term 2012/1433

Course Code: CPCS-203 Course Name: Programming II
______________________________________________________________________

Objectives
In this chapter you will learn:
What arrays are.
To use arrays to store data in and retrieve data from lists and tables of values.
To declare an array, initialize an array and refer to individual elements of an array.
To use the enhanced for statement to iterate through arrays.
To pass arrays to methods.
To declare and manipulate multidimensional arrays.
To write methods that use variable-length argument lists.
To read command-line arguments into a program.


Prelab Activity:

Matching
The questions are intended to test and reinforce your understanding of key concepts. You may
answer the questions before the lab.

For each term in the left column, write the letter for the description from the right column that
best matches theterm.

Term Description

_1. pass by value a) Indicates that a method receives a variable
number
of arguments.

_2. a[ i ][ j ] b) Declares an array of type int.

_3. index c) A collection of variables that contain values
of thesame type.

_4. new int[ 12 ] d) Iterates through an array without using a
counter.

_5. ... e) Information passed to an application when it
executes.

_6. pass by reference f) A copy of the argument’s value is made and
passedto the called method.

_7. array g) Represented by an array with two
dimensions.

_8. enhanced for statement h) A calling method gives a called method the
ability to access and potentially modify the
caller’s data directly.

_9. int c[] i) One element of an array with two
dimensions.

_10. tables of values j) Specifies a particular element in an array.

_11. length k) Creates an array of integers.

_12. command-line arguments l) An array member that contains the number
of elements in an array.


Prelab Activity:

Fill in the Blank

Fill in the blanks for each of the following statements:
13. Every array has a(n) ________ member that specifies the number of elements in the array.
14. When an argument is ________, a copy of the argument’s value is made and passed to the
called method.
15. To pass an array to a method, you must specify the ________ of the array as an argument in
the method call.
16. An array ________ may be an integer or an integer expression.
17. The first element in every array has index ________.
18. A(n) ________argument list is treated as an array within the method declaration’s body.
19. Arrays are ________entities—they remain the same length once they are created.
20. ________must be initialized before they are used and cannot be modified thereafter.
21. To pass one row of a two-dimensional array to a method that receives a one-dimensional
array, you specifythe array’s ________ followed by only the row ________

Prelab Activity:


Short Answers
22. What is an off-by-one error?

23. What benefits does the enhanced for statement provide for array processing? What are its
limitations?

24. Why are command-line arguments passed to the main method as Strings? What problems
would arise ifcommand-line arguments were passed using an array of doubles?

25. Describe how two-dimensional arrays represent a table of data.

26. Differentiate between pass-by-value and pass-by-reference.

Prelab Activity:


Program Output
For each of the given program segments, read the code, and write the output in the space
provided below eachprogram. [Note: Do not execute these programs on a computer.]
Unless specified otherwise, for the following questions assume that the code segments are
contained within themain method of a Java application.

27. What is the output of the following code segment?

1 int array[] = { 8, 6, 9, 7, 6, 4, 4, 5, 8, 10 };
2 System.out.println("Index Value" );
3
4 for ( inti = 0; i < array.length; i++ )
5 System.out.printf("%d %dn", i, array[ i ] );

Your answer:


1 char sentence[] = { 'H', 'o', 'w', ' ', 'a', 'r', 'e', ' ', 'y', 'o', 'u' };
2 String output = "The sentence is: ";
3
4 for ( inti = 0; i < sentence.length; i++ )
5 System.out.printf("%c ", sentence[ i ] );
6
7 System.out.println();

Your answer:


1 int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };


2
3 for ( inti = 0; i < array.length; i++ )
4{
5 for ( intj = 0; j < array [ i ]; j++ )
6 System.out.print("*" );
7
8System.out.println();
9}

Your answer:


1 int array[] = { 3, 2, 5 };
2
3 for ( inti = 0; i <3; i++ )
4 array[ i ] *= 2;
5
6for ( intj : array )
7 System.out.print("%d ", j );
8

Your answer:

Given the following declaration of a method

1 public int method1(int... values )
2{
3 int mystery = 1;
4
5for ( inti : values )
6 mystery *= i;
7
8return mystery;
9}

1 System.out.println( method1( 1, 2, 3, 4, 5 ) );

Your answer:


Given the following declaration of a method

1 public int method1(int values[][] )
2{
3 int mystery = 1;
4
5for ( inti[] : values )
6 for ( intj : i )
7 mystery *= j;
8
9return mystery;
10 }


1 int array[][] = { { 3, 2, 5 }, { 2, 2, 4, 5, 6 }, { 1, 1 } };
2
3System.out.println( mystery( array ) );

Your answer:

Prelab Activity:


Correct the Code
Determine if there is an error in each of the following program segments. If there is an error,
specify whether itis a logic error or a compilation error, circle the error in the program and write
the corrected code in the spaceprovided after each problem. If the code does not contain an error,
write “no error.” [Note: There may be morethan one error in each program segment.]

33. The following code segment should assign 8 to the element of integer array with index 10.

1 array(10 ) = 8;

Your answer:

34. The forstatement that follows should initialize all of array’s elements to -1.

1 int array[] = new int[ 10 ];
2
3 for ( inti = 0; i <9; i++ )
4 array[ i ] = -1;

Your answer:

35. Array a should contain all the integers from 0 through 10, inclusive.

1 int a[] = new int[ 10 ];


2
3 for ( inti = 0; i <10; i++ )
4 a[ i ] = i;

Your answer:

36. The following code segment should allocate two arrays containing five and six elements,
respectively.

1 final int arraySize = 5;
2
3 int a[] = new int[ arraySize ];
4
5arraySize = 6;
6
7 int b[] = new int[ arraySize ];

Your answer:

37. The following code segment should initialize a two-dimensional array, then print its values.

1 int a[][] = new int[ 10 ][ 5 ];


2
3 for ( inti = 0; i < a.length; i++ )
4 for ( intj = 0; j < a[ i ].length; j++ )
5 a[ j ][ i ] = j;
6
7 for ( inti = 0; i < a.length; i++ )
8{
9 for ( intj = 0; j < a[ i ].length; j++ )
10 System.out.printf("%d ", a[ j ][ i ] );
11
12 System.out.println();
13 }

Your answer:

38. The following code segment should assign the value 10 to the array element that corresponds
to the thirdrow and the fourth column.

1 int a[] = new int[ 10 ][ 5 ];
2
3 a[2 ][ 3 ] = 10;

Your answer:

Lab Exercises:


Lab Exercise 1 — Duplicate Elimination

This problem is intended to be solved in a closed-lab session with a teaching assistant or
instructor present. Theproblem is divided into six parts:
1. Lab Objectives
2. Description of Problem
3. Sample Output
4. Program Template (Figure 1: )
5. Problem-Solving Tips
6. Follow-Up Questions and Activities

The program template represents a complete working Java program, with one or more key lines
of code replacedwith comments. Read the problem description and examine the sample output;
then study the template code.
Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile
and execute thesource code for the template is available at www.pearsonhighered.com/deitel

Lab Objectives
In thislab, you will practice:
Declaring and initializing arrays.
Comparing input to array elements.
Preventing array out-of-bounds errors.

The follow-up questions and activities will also give you practice:
Initializing array sizes during program execution.
Generalizing programs.

Description of the Problem
Use a one-dimensional array to solve the following problem: Write an application that inputs five
numbers, eachof which is between 10 and 100, inclusive. As each number is read, display it only
if it is not a duplicate of a numberalready read. Provide for the “worst case,” in which all five
numbers are different. Use the smallest possiblearray to solve this problem. Display the complete
set of unique values input after the user inputs each new value.

Sample Output

Enter number: 11
11
Enter number: 85
11 85
Enter number: 26
11 85 26
Enter number: 11
11 has already been entered


Program Template
1 // Lab 1: Unique.java
2 // Reads in 5 unique numbers.
3 import java.util.Scanner;
4
5 public classUniqueTest
6{
7 public static void main( String args[] )
8{
9 getNumbers();
11} // end main
12
13// gets 5 unique numbers from the user
14public void getNumbers()
15 {
16Scanner input = new Scanner( System.in );
17
18/* Create an array of five elements*/
19int count = 0; // number of uniques read
20int entered = 0; // number of entered numbers
21
22while( entered < numbers.length )
23{
24 System.out.print("Enter number: " );
25 /* Write code here to retrieve the input from the user */
26
27 // validate the input
28 /* Write an if statement that validates the input */
29 {
30 // flags whether this number already exists
31 booleancontainsNumber = false;
32
33 // increment number of entered numbers
34 entered++;
35
36/* Compare the user input to the unique numbers in the array using a for
37statement. If the number is unique, store new number */
38
39/* add the user input to the array only if the number is not already
40in the array */
41if ( !containsNumber )


42{
43/* Write code to add the number to the array and increment
44unique items input */
45}// end if
46else
47System.out.printf("%d has already been enteredn",
48number );
49}// end if
50else
51System.out.println("number must be between 10 and 100" );
52
53// print the list of unique values
54/* Write code to output the contents of the array */
55}// end while
56}// end method getNumbers
57}// end class UniqueTest

Figure 1: Unique.java

Problem-Solving Tips
1. Initialize the integer array numbers to hold five elements. This is the maximum number of
values the program must store if all values input are unique.
2. Remember to validate the input and display an error message if the user inputs invalid data.
3. If the number entered is not unique, display a message to the user; otherwise, store the
number in the array and display the list of unique numbers entered so far.
4. If you have any questions as you proceed, ask your lab instructor for assistance.

Follow-Up Questions and Activities
1. Modify the program in Lab Exercise 1 to input 30 numbers, each of which is between 10 to
500, inclusive.


2. Modify the program in Follow-Up Question 1 to allow the user to enter numbers until the
array is full.

3. Modify your solution to Follow-Up Question 2 to allow the user to enter the size of the array
as the application begins execution.

Lab Exercises:

Lab Exercise 2 — Craps Game
This problem is intended to be solved in a closed-lab session with a teaching assistant or
instructor present. Theproblem is divided into five parts:
1. Lab Objectives
2. Description of Problem


3. Sample Output
4. Program Template (Figure 2)
5. Problem-Solving Tips

The program template represents a complete working Java program, with one or more key lines
of code replacedwith comments. Read the problem description and examine the sample output;
then study the template code.
Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile
and execute theprogram. Compare your output with the sample output provided. The source code
for the template is availableat www.pearsonhighered.com/deitel

Lab Objectives
In thislab you will practice:
Declaring and initializing arrays.
Using arrays to store sets of data.

Description of the Problem
Write an application that runs 1000 games of craps and answers the following questions:
a) How many games are won on the first roll, second roll, …, twentieth roll and after the
twentieth roll?
b) How many games are lost on the first roll, second roll, …, twentieth roll and after the
twentieth roll?
c) What are the chances of winning at craps? [Note: You should discover that craps is one
of the fairest casino games. What do you suppose this means?]
d) What is the average length of a game of craps?

Sample Output

224 games won and 99 games lost on roll #1


Program Template
1 // Lab 2: CrapsTest.java
2 // Program plays 1000 games of craps and displays winning
3 // and losing statistics.
4 import java.util.Random;
5
6public classCrapsTest
7{
8public static void main( String args[] )
9{
10 // create random number generator for use in method rollDice
11 private static Random randomNumbers = new Random();
12
13 // enumeration with constants that represent the game status
14 private enum Status { CONTINUE, WON, LOST };
15
16 /* Declare array to store the number of games won by number of rolls in the
17 game */
18 /* Declare array to store the number of games lost by number of rolls in the game
19 */
20 int winSum = 0; // total number of wins
21 int loseSum = 0; // total number of losses
22
23 // plays one game of craps
24 `play();
25}// end main
26
27
28public void play()
29{
30int sumOfDice = 0; // sum of the dice
31int myPoint = 0; // point if no win or loss on first roll
32
33Status gameStatus; // can contain CONTINUE, WON or LOST
34
35int roll; // number of rolls for the current game
36
37/* Create the array to store the number of games won */


38/* Create the array to store the number of games lost */
39
40for ( inti = 1; i <= 1000; i++ )
41{
42sumOfDice = rollDice(); // first roll of the dice
43roll = 1;
44
45// determine game status and point based on sumOfDice
46switch ( sumOfDice )
47{
48case 7: // win with 7 on first roll
49case 11: // win with 11 on first roll
50gameStatus = Status.WON;
51break;
52case 2: // lose with 2 on first roll
55gameStatus = Status.LOST;
56break;
57default: // did not win or lose, so remember point
58gameStatus = Status.CONTINUE; // game is not over
59myPoint = sumOfDice; // store the point
60break; // optional for default case at end of switch
61}// end switch
62
63// while game is not complete ...
64while ( gameStatus == Status.CONTINUE )
65{
66sumOfDice = rollDice(); // roll dice again
67roll++;
68
69// determine game status
70if ( sumOfDice == myPoint ) // win by making point
71gameStatus = Status.WON;
72else if ( sumOfDice == 7 ) // lose by rolling 7
73gameStatus = Status.LOST;
74}// end while
75
76// all roll results after 20th roll placed in last element
77/* Write an if statement to test whether the number of rolls is greater than
7821 and, if true, set number of rolls to 21 */
79
80// increment number of wins in that roll
81if ( gameStatus == Status.WON )
82{
83/* Write code to increment the number of games won for a
84specific number of rolls */
85/* Write code to increment the overall number of games won */
86}// end if
87else // increment number of losses in that roll
88{
89/* Write code to increment the number of games lost for a
90specific number of rolls */
91/* Write code to increment the overall number of games lost */
92}// end else
93}// end for


94
95printStats();
96}// end method play
97
98// print win/loss statistics
99public void printStats()
100{
101int totalGames = winSum + loseSum; // total number of games
102int length = 0; // total length of the games
103
104// display number of wins and losses on all rolls
105for ( inti = 1; i <= 21; i++ )
106{
107/* Write an if statement to test whether i is equal to 21 */
108/* Output number of games won and lost after the 20th roll */
109else
110/* Output number of games won and lost after each roll less than 20 */
111
112// calculate total number of rolls to win/lose all games
113// add number of wins by number of rolls needed to win
114// add number of losses by number of rolls needed to lose
115/* Write code to calculate total length of games */
116}// end for
117
118// calculate chances of winning
119System.out.printf("n%s %d / %d = %.2f%%n",
120"The chances of winning are", winSum, totalGames,
121( 100.0* winSum / totalGames ) );
122
123
124System.out.printf("The average game length is %.2f rolls.n",
125( (double ) length / totalGames ) );
126}// end method printStats
127
128// roll dice, calculate sum and display results
129public int rollDice()
130{
131// pick random die values
132int die1 = 1 + randomNumbers.nextInt(6 );
133int die2 = 1 + randomNumbers.nextInt(6 );
134int sum = die1 + die2; // sum die values
135
136return sum; // return sum of dice
137}// end method rollDice
138} // end class CrapsTest

Problem-Solving Tips
1. The arrays to hold the number of wins and losses by number of rolls should have 22
elements. We are keeping track of the number of wins and losses decided on the first through
twentieth roll along with games decided after the twentieth roll. That requires 21 elements.


The extra element is because arrays begin with element zero. This element will not hold any
information in the program.
2. To calculate the total number of rolls, multiply each index in the arrays by the value of that
element in the array.
3. If you have any questions as you proceed, ask your lab instructor for assistance.

Lab Exercises:

Debugging
The program in this section does not run properly. Fix all the compilation errors, so that the
program will compilesuccessfully. Once the program compiles, compare the output to the sample
output, and eliminate any logicerrors that exist. The sample output demonstrates what the


program’s output should be once the program’s codeis corrected. The file is available at
www.deitel.com/books/jhtp8/ and at www.pearsonhighered.com/deitel.

Sample Output
Enter sales person number (-1 to end): 1
Enter product number: 4
Enter sales amount: 1082
Enter sales person number (-1 to end): -1
Product Salesperson 1 Salesperson 2 Salesperson 3 Salesperson 4 Total
1 0.00 0.00 678.00 1554.00 2232.00
2 0.00 0.00 0.00 0.00 0.00
3 0.00 998.00 0.00 0.00 998.00
4 1082.00 0.00 0.00 0.00 1082.00
5 0.00 0.00 0.00 0.00 0.00
Total 1082.00 998.00 678.00 1554.00

Broken Code
1 // Debugging Problem Chapter 7: Sales2.java
2 // Program totals sales for salespeople and products.
3 import java.util.Scanner;
4
5// Debugging Problem Chapter 7: Sales2Test.java
6// Test application for class Sales2
7public classSales2Test
8{
9public static void main( String args[] )
10{
11 calculateSales();
12}// end main
13
14 Scanner input = new Scanner( System.in );
15 // sales array holds data on number of each product sold
16 // by each salesman
17 double sales = new double[5 ][ 4 ];
18
19 System.out.print("Enter sales person number (-1 to end): " );
20 int person = input.nextInt();
21
22 while ( person != -1 )
23 {
24 System.out.print("Enter product number: " );


25 int product = input.next();
26 System.out.print("Enter sales amount: " );
27 double amount = input.nextDouble();
28
29 // error-check the input
30 if ( person<1 && person >5 &&
31 product >= 1 && product <6 && amount >= 0 )
32 sales[ product - 1 ][ person - 1 ] += amount;
33 else
34 System.out.println("Invalid input!" );
35
36 System.out.print("Enter sales person number (-1 to end): " );
37 person = input.nextInt();
38 } // end while
39
40 // total for each salesperson
41 double salesPersonTotal[][] = new double[ 4 ];
42
43 // display the table
44 for ( intcolumn = 0; column <4; column++ )
45 salesPersonTotal[ column ][ row ] = 0;
46
47 System.out.printf("%7s%14s%14s%14s%14s%10sn",
48 "Product", "Salesperson 1", "Salesperson 2",
49 "Salesperson 3", "Salesperson 4", "Total" );
50
51 // for each column of each row, print the appropriate
52 // value representing a person's sales of a product
53 for ( introw = 0; row <5; row++ )
54 {
55 double productTotal = 0.0;
56 System.out.printf("%7d", ( row + 1 ) );
57
58 for ( intcolumn = 0; column <4; column++ ) {
59 System.out.printf("%14.2f", sales[ column ][ row ] );
60 productTotal += sales[ column ][ row ];
61 salesPersonTotal[ column ] += sales[ column ][ row ];
62 } // end for
63
64 System.out.printf("%10.2fn", productTotal );
65} // end for
66
67System.out.printf("%7s", "Total" );
68
69for ( intcolumn = 0; column <4; column++ )
70System.out.printf("%14.2f", salesPersonTotal[ column ] );
71
73}// end method calculateSales
64}// end class Sales2Test


Postlab Activities

Topics
Lab Exercises

One-Dimensional Arrays Tracking Sales


Grading Quizzes
Reversing an Array
Adding To and Removing From an Integer List

Command Line Arguments Averaging Numbers

Variable Length Parameter Lists Exploring Variable Length Parameter Lists

Two-Dimensional Arrays Matrix Inverse

Coding Exercise 1
Tracking Sales
File Sales.java contains a Java program that prompts for and reads in the sales for each of 5
salespeople in a company. It thenprints out the id and amount of sales for each salesperson and
the total sales. Study the code, then compile and run theprogram to see how it works. Now
modify the program as follows:
1. Compute and print the average sale. (You can compute this directly from the total; no loop is
necessary.)
2. Find and print the maximum sale. Print both the id of the salesperson with the max sale and
the amount of the sale, e.g., “Salesperson 3 had the highest sale with $4500.” Note that you
don’t need another loop for this; you can do it in the same loop where the values are read and
the sum is computed.
3. Do the same for the minimum sale.
4. After the list, sum, average, max and min have been printed; ask the user to enter a value.
Then print the id of each salesperson who exceeded that amount, and the amount of their
sales. Also print the total number of salespeople whose sales exceeded the value entered.
5. The salespeople are objecting to having an id of 0—no one wants that designation. Modify
your program so that the ids run from 1-5 instead of 0-4. Do not modify the array—just
make the information for salesperson 1 resides in array location 0, and so on.
6. Instead of always reading in 5 sales amounts, at the beginning ask the user for the number of
sales people and then createan array that is just the right size. The program can then proceed
as before.

// ***************************************************************
// Sales.java
//
// Reads in and stores sales for each of 5 salespeople. Displays
// sales entered by salesperson id and total sales for all salespeople.
//
// ***************************************************************
import java.util.Scanner;
public class Sales


{
public static void main(String[] args)
{
final int SALESPEOPLE = 5;
int[] sales = new int[SALESPEOPLE];
int sum;
Scanner scan = new Scanner(System.in);
for (int i=0; i<sales.length; i++)
{
System.out.print("Enter sales for salesperson " + i + ": ");
sales[i] = scan.nextInt();
}
System.out.println("nSalesperson Sales");
System.out.println(" ------------------ ");
sum = 0;
for (int i=0; i<sales.length; i++)
{
System.out.println(" " + i + " " + sales[i]);
sum += sales[i];
}
System.out.println("nTotal sales: " + sum);
}
}

Postlab Activities

Coding Exercise 2
Grading Quizzes
Write a program that grades arithmetic quizzes as follows:


1. Ask the user how many questions are in the quiz.
2. Ask the user to enter the key (that is, the correct answers). There should be one answer for
each question in the quiz, and each answer should be an integer. They can be entered on a
single line, e.g., 34 7 13 100 81 3 9 10 321 12 might be the key for a 10-question quiz. You
will need to store the key in an array.
3. Ask the user to enter the answers for the quiz to be graded. As for the key, these can be
entered on a single line. Again there needs to be one for each question. Note that these
answers do not need to be stored; each answer can simply be compared to the key as it is
entered.
4. When the user has entered all of the answers to be graded, print the number correct and the
percent correct.

When this works, add a loop so that the user can grade any number of quizzes with a single key.
After the results have been printed for each quiz, ask “Grade another quiz? (y/n).”

Postlab Activities

Coding Exercise 3
Reversing an Array


Write a program that prompts the user for an integer, and then asks the user to enter that many
values. Store these values in anarray and print the array. Then reverse the array elements so that
the first element becomes the last element, the secondelement becomes the second to last
element, and so on, with the old last element now first. Do not just reverse the order inwhich
they are printed; actually change the way they are stored in the array. Do not create a second
array; just rearrange theelements within the array you have. (Hint: Swap elements that need to
change places.) When the elements have beenreversed, print the array again.

Postlab Activities

Coding Exercise 4

Averaging Numbers


When you run a Java program called Foo, anything typed on the command lineafter “java Foo”
is passed to the main method in the args parameter as an array of strings.
1. Write a program Average.java that just prints the strings that it is given at the command line,
one per line. If nothingis given at the command line, print “No arguments”.
2. Modify your program so that it assumes the arguments given at the command line are
integers. If there are noarguments, print a message. If there is at least one argument, compute
and print the average of the arguments. Notethat you will need to use the parseInt method of
the Integer class to extract integer values from the strings that arepassed in. If any non-
integer values are passed in, your program will produce an error, which is unavoidable at
thispoint.

Postlab Activities

Coding Exercise 5
Exploring Variable Length Parameter Lists


The file Parameters.java contains a program to test the variable length method average from
Section 7.5 of the text. Notethat average must be a static method since it is called from the static
method main.
1. Compile and run the program. You must use the -source 1.5 option in your compile
command.
2. Add a call to find the average of a single integer, say 13. Print the result of the call.
3. Add a call with an empty parameter list and print the result. Is the behavior what you
expected?
4. Add an interactive part to the program. Ask the user to enter a sequence of at most 20
nonnegative integers. Yourprogram should have a loop that reads the integers into an array
and stops when a negative is entered (the negativenumber should not be stored). Invoke the
average method to find the average of the integers in the array (send thearray as the
parameter). Does this work?
5. Add a method minimum that takes a variable number of integer parameters and returns the
minimum of theparameters. Invoke your method on each of the parameter lists used for the
average function.

//*******************************************************
// Parameters.java
//
// Illustrates the concept of a variable parameter list.
//*******************************************************
import java.util.Scanner;
public class Parameters
{
//-----------------------------------------------
// Calls the average and minimum methods with
// different numbers of parameters.
//-----------------------------------------------
public static void main(String[] args)
{
double mean1, mean2;
mean1 = average(42, 69, 37);
mean2 = average(35, 43, 93, 23, 40, 21, 75);
System.out.println ("mean1 = " + mean1);
System.out.println ("mean2 = " + mean2);
}
//----------------------------------------------
// Returns the average of its parameters.
//----------------------------------------------
public static double average (int ... list)
{
double result = 0.0;
if (list.length != 0)
{
int sum = 0;
for (int num: list)
sum += num;
result = (double)sum / list.length;
}
return result;
}
}


Postlab Activities

Coding Exercise 6
Matrix Inverse


The inverse of a square matrix A is denoted A-1, such that A×A-1 = I, where I is the identity
matrix with all1’s on the diagonal and 0 on all other cells.
1 2 1 2 0.5 0.5
2 3 1 1 0.5 0.5
4 5 3 1 1.5 0.5
The inverse of matrix , for example, is

that is,

1 2 1 2 0.5 0.5 1 0 0
2 3 1 1 0.5 0.5 0 1 0
4 5 3 1 1.5 0.5 0 0 1

The inverse of a 3 × 3 matrix
a11 a12 a13
A a 21 a 22 a 23
a 31 a 32 a 33
can be obtained using the following formula if | A | 0 :

a 22 a 33 a 23a 32 a13a 32 a12 a 33 a12 a 23 a13a 22
1 1
A a 23a 31 a 21a 33 a11a 33 a13 a 31 a13a 21 a11a 23
| A|
a 21a 32 a 22 a 31 a12 a 31 a11a 32 a11a 22 a12 a 21

a11 a12 a13
| A | a 21 a 22 a 23 a11a 22 a 33 a 31a12 a 23 a13a 21a 32 a13 a 22 a 31 a11a 23 a 32 a 33 a 21a12
a 31 a 32 a 33
.

Implement the following function to obtain an inverse of the matrix:

public static double[][] inverse(double[][] A)

a a a a a
Write a test program that prompts the user to enter a11 , a12 , 13 , a 21 , a 21 , 23 , 31 , 32 , 33 for
a matrix and displays its inverse matrix. Here are the sample runs:

Sample 1
Enter a11, a12, a13, a21, a22, a23, a31, a32, a33: 1 2 1 2 3 1 4 5 3
-2 0.5 0.5
1 0.5 -0.5
1 -1.5 0.5

Sample 2
Enter a11, a12, a13, a21, a22, a23, a31, a32, a33: 1 4 2 2 5 8 2 1 8


2.0 -1.875 1.375
0.0 0.25 -0.25
-0.5 0.4375 -0.1875

Cpcs 203 -array-problems

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