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Sarah Akinkunmi
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‎src/chapter4/CheckerboardPatternOfAsterisks.java‎

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/*
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4.32 (Checkerboard Pattern of Asterisks) Write an application that uses only the output statements
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System.out.print("* ");
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System.out.print(" ");
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System.out.println();
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to display the checkerboard pattern that follows. A System.out.println method call with no arguments causes the program to output a single newline character. [Hint: Repetition statements are
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required.]
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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* * * * * * * *
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*/
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package chapter4;
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import java.util.Scanner;
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public class CheckerboardPatternOfAsterisks {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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int size = input.nextInt();
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int lines = size;
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for(int i = 0; i < lines; i++) {
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if(i % 2 == 0) {
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for(int shape = 0; shape < size; shape++) {
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System.out.print("* ");
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System.out.print(" ");
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}
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} else if (i % 2 != 0) {
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for(int shape = 0; shape < size; shape++) {
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System.out.print(" ");
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System.out.print("* ");
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}
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}
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System.out.println();
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}
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}
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}

‎src/chapter4/CreditLimitCalculator.java‎

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/*
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4.18 (Credit Limit Calculator) Develop a Java application that determines whether any of several
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department-store customers has exceeded the credit limit on a charge account. For each customer,
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the following facts are available:
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a) account number
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b) balance at the beginning of the month
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c) total of all items charged by the customer this month
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d) total of all credits applied to the customer’s account this month
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e) allowed credit limit
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The program should input all these facts as integers, calculate the new balance (= beginning balance
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+ charges – credits), display the new balance and determine whether the new balance exceeds the
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customer’s credit limit. For those customers whose credit limit is exceeded, the program should display the message "Credit limit exceeded".
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*/
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package chapter4;
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import java.util.Scanner;
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public class CreditLimitCalculator {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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int accountNumber;
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int balance;
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int totalCharges;
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int totalCredits;
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int creditLimit;
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System.out.println("Enter customer's account number: ");
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accountNumber = input.nextInt();
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System.out.println("Enter customer's beginning balance: ");
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balance = input.nextInt();
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System.out.println("Enter total of all items charged by customer this month: ");
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totalCharges = input.nextInt();
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System.out.println("Enter total of all credits applied to the customer’s account this month: ");
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totalCredits = input.nextInt();
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System.out.println("Enter credit limit applicable to customer: ");
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creditLimit = input.nextInt();
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while (creditLimit > balance) {
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balance += totalCredits - totalCharges;
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System.out.println("The customer's new balance is " + balance);
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}
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if(balance > creditLimit)
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System.out.println("Credit Limit Exceeded!");
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}
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}

‎src/chapter4/DecimalEquivalentOfBinary.java‎

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/*
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4.31 (Printing the Decimal Equivalent of a Binary Number) Write an application that inputs an
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integer containing only 0s and 1s (i.e., a binary integer) and prints its decimal equivalent. [Hint: Use
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the remainder and division operators to pick off the binary number’s digits one at a time, from right
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to left. In the decimal number system, the rightmost digit has a positional value of 1 and the next
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digit to the left a positional value of 10, then 100, then 1000, and so on. The decimal number 234
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can be interpreted as 4 * 1 + 3 * 10 + 2 * 100. In the binary number system, the rightmost digit has
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a positional value of 1, the next digit to the left a positional value of 2, then 4, then 8, and so on.
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The decimal equivalent of binary 1101 is 1 * 1 + 0 * 2 + 1 * 4 + 1 * 8, or 1 + 0 + 4 + 8 or, 13.]
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*/
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package chapter4;
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import java.util.Scanner;
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public class DecimalEquivalentOfBinary {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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int binaryNumber = input.nextInt();
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int decimalNumber = 0;
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if(binaryNumber >= 10 && binaryNumber <= 99) {
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int firstDigit = binaryNumber % 10;
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int secondDigit = binaryNumber / 10;
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if(firstDigit == 1 || firstDigit == 0 && (secondDigit == 1 || secondDigit == 0)) {
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decimalNumber = firstDigit + secondDigit * 2;
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}
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System.out.println("The decimal equivalent of " + binaryNumber + "is " + decimalNumber);
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} else if(binaryNumber >= 100 && binaryNumber <= 999) {
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int firstDigit = binaryNumber % 10;
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int secondDigit = binaryNumber / 10 % 10;
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int thirdDigit = binaryNumber / 100;
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if(firstDigit == 1 || firstDigit == 0 && (secondDigit == 1 || secondDigit == 0) && (thirdDigit == 1 || thirdDigit == 0)) {
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decimalNumber = firstDigit + secondDigit * 2 + thirdDigit * 4;
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}
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System.out.println("The decimal equivalent of " + binaryNumber + " is " + decimalNumber);
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} else if(binaryNumber >= 1000 && binaryNumber <= 9999) {
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int firstDigit = binaryNumber % 10;
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int secondDigit = binaryNumber / 10 % 10;
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int thirdDigit = binaryNumber / 100 % 10;
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int fourthDigit = binaryNumber / 1000;
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if(firstDigit == 1 || firstDigit == 0 && (secondDigit == 1 || secondDigit == 0) && (thirdDigit == 1 || thirdDigit == 0) && (fourthDigit == 1 || fourthDigit == 0)) {
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decimalNumber = firstDigit + secondDigit * 2 + thirdDigit * 4 + fourthDigit * 8;
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}
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System.out.println("The decimal equivalent of " + binaryNumber + " is " + decimalNumber);
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} else if(binaryNumber >= 10000 && binaryNumber <= 99999) {
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int firstDigit = binaryNumber % 10;
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int secondDigit = binaryNumber / 10 % 10;
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int thirdDigit = binaryNumber / 100 % 10;
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int fourthDigit = binaryNumber / 1000 % 10;
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int fifthDigit = binaryNumber / 10000;
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if (firstDigit == 1 || firstDigit == 0 && (secondDigit == 1 || secondDigit == 0) && (thirdDigit == 1 || thirdDigit == 0) && (fourthDigit == 1 || fourthDigit == 0) && (fifthDigit == 1 || fifthDigit == 0)) {
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decimalNumber = firstDigit + secondDigit * 2 + thirdDigit * 4 + fourthDigit * 8 + fifthDigit * 16;
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}
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System.out.println("The decimal equivalent of " + binaryNumber + " is " + decimalNumber);
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} else {
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System.out.println("Number is not a binary number");
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}
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}
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}

‎src/chapter4/Decrypting.java‎

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package chapter4;
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public class Decrypting {
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public void decoder(int userInput){
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int decryptedFirstDigit = 0;
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int decryptedSecondDigit = 0;
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int decryptedThirdDigit = 0;
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int decryptedFourthDigit = 0;
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int encryptedFirstDigit = userInput % 100 / 10;
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int encryptedSecondDigit = userInput % 10;
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int encryptedThirdDigit = userInput / 1000;
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int encryptedFourthDigit = userInput % 1000 / 100;
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for(int possibleAnswer = 0; possibleAnswer <= 9; possibleAnswer++){
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if ((possibleAnswer + 7) % 10 == encryptedFirstDigit){ decryptedFirstDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedSecondDigit){ decryptedSecondDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedThirdDigit){ decryptedThirdDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedFourthDigit){ decryptedFourthDigit = possibleAnswer; }
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}
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int decryptedInteger = (decryptedFirstDigit * 1000 + decryptedSecondDigit * 100 + decryptedThirdDigit * 10 + decryptedFourthDigit);
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System.out.println(decryptedInteger);
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}
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}

‎src/chapter4/DecryptingTest.java‎

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package chapter4;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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public class DecryptingTest {
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private Decrypting decoder;
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@BeforeEach
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void startTestsWith() {
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decoder = new Decrypting();
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}
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@Test
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void testThatUserInputsFourDigitNumber(){
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decoder.decoder(1234);
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}
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}

‎src/chapter4/Decryptor.java‎

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/*
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4.38 (Enforcing Privacy with Cryptography) The explosive growth of Internet communications
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and data storage on Internet-connected computers has greatly increased privacy concerns. The field
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of cryptography is concerned with coding data to make it difficult (and hopefully—with the most
5+
advanced schemes—impossible) for unauthorized users to read. In this exercise you’ll investigate a
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simple scheme for encrypting and decrypting data. A company that wants to send data over the Internet
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has asked you to write a program that will encrypt it so that it may be transmitted more securely.
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All the data is transmitted as four-digit integers. Your application should read a four-digit
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integer entered by the user and encrypt it as follows: Replace each digit with the result of adding 7
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to the digit and getting the remainder after dividing the new value by 10. Then swap the first digit
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with the third, and swap the second digit with the fourth. Then print the encrypted integer. Write
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a separate application that inputs an encrypted four-digit integer and decrypts it (by reversing the
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encryption scheme) to form the original number. [Optional reading project: Research “public key
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cryptography” in general and the PGP (Pretty Good Privacy) specific public key scheme. You may
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also want to investigate the RSA scheme, which is widely used in industrial-strength applications.]
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*/
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package chapter4;
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import java.util.Scanner;
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public class Decryptor {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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System.out.println("Enter a four-digit number: ");
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int initialNumber = input.nextInt();
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int decryptedFirstDigit = 0;
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int decryptedSecondDigit = 0;
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int decryptedThirdDigit = 0;
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int decryptedFourthDigit = 0;
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int encryptedFirstDigit = initialNumber % 100 / 10;
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int encryptedSecondDigit = initialNumber % 10;
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int encryptedThirdDigit = initialNumber / 1000;
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int encryptedFourthDigit = initialNumber % 1000 / 100;
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for(int possibleAnswer = 0; possibleAnswer <= 9; possibleAnswer++){
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if ((possibleAnswer + 7) % 10 == encryptedFirstDigit){ decryptedFirstDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedSecondDigit){ decryptedSecondDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedThirdDigit){ decryptedThirdDigit = possibleAnswer; }
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if ((possibleAnswer + 7) % 10 == encryptedFourthDigit){ decryptedFourthDigit = possibleAnswer; }
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}
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int decryptedInteger = (decryptedFirstDigit * 1000 + decryptedSecondDigit * 100 + decryptedThirdDigit * 10 + decryptedFourthDigit);
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System.out.println("The decrypted number is " + decryptedInteger);
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}
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}

‎src/chapter4/DoWhileStudentAverageGrade.java‎

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package chapter4;
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import java.util.Scanner;
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public class DoWhileStudentAverageGrade {
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public static void main(String[] args){
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Scanner input = new Scanner(System.in);
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int studentGrade;
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int totalGrade = 0;
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int numberOfGrades = 0;
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do{
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System.out.print("Enter student grade: ");
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studentGrade = input.nextInt();
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totalGrade += studentGrade;
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numberOfGrades++;
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}
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while(numberOfGrades < 10);
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System.out.print(totalGrade);
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double averageGrade = totalGrade / (numberOfGrades * 1.0);
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System.out.println(averageGrade);
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}
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}

‎src/chapter4/EConstantFactorial.java‎

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/*
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4.37 (Factorial) The factorial of a non-negative integer n is written as n!
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(pronounced “n factorial”) and is defined as follows
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n! = n · (n – 1) · (n – 2) · … · 1 (for values of n greater than or equal to 1)
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and
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n! = 1 (for n = 0)
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For example, 5! = 5 · 4 · 3 · 2 · 1, which is 120.
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b) Write an application that estimates the value of the mathematical constant e by using
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the following formula. Allow the user to enter the number of terms to calculate.
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e = 1 + 1/1! + 1/2! + 1/3!...
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c) Write an application that computes the value of e^(x)nby using the following formula. Allow the user to enter the number of terms to calculate.
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e^(x) = 1 + x/1! + x^2/2! + x^3/3!...
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*/
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package chapter4;
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public class EConstantFactorial {
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public static int factorial(int n) {
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int i = 1;
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int solution = 1;
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while (i <= n) {
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solution = solution * i;
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i++;
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}
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return solution;
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}
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public static double getEConstant(int userConstraint) {
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double e = 1;
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for(int i = 1; i <= userConstraint; i++)
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e += 1.0 / factorial(i);
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return e;
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}
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public static double getEConstantToAPower(int userConstraint, int power) {
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double e = 1;
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for(int i = 1; i <= userConstraint; i++)
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e += Math.pow(power, i) / factorial(i);
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return e;
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}
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}
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‎src/chapter4/EConstantFactorialTest.java‎

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package chapter4;
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public class EConstantFactorialTest {
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public static void main(String[] args) {
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System.out.printf("%s%f%n", "The value of e is ", EConstantFactorial.getEConstant(3));
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System.out.printf("%s%f", "The value of e^(2) is ", EConstantFactorial.getEConstantToAPower(3, 2));
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}
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}

‎src/chapter4/Encryptor.java‎

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/*
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4.38 (Enforcing Privacy with Cryptography) The explosive growth of Internet communications
3+
and data storage on Internet-connected computers has greatly increased privacy concerns. The field
4+
of cryptography is concerned with coding data to make it difficult (and hopefully—with the most
5+
advanced schemes—impossible) for unauthorized users to read. In this exercise you’ll investigate a
6+
simple scheme for encrypting and decrypting data. A company that wants to send data over the Internet
7+
has asked you to write a program that will encrypt it so that it may be transmitted more securely.
8+
All the data is transmitted as four-digit integers. Your application should read a four-digit
9+
integer entered by the user and encrypt it as follows: Replace each digit with the result of adding 7
10+
to the digit and getting the remainder after dividing the new value by 10. Then swap the first digit
11+
with the third, and swap the second digit with the fourth. Then print the encrypted integer. Write
12+
a separate application that inputs an encrypted four-digit integer and decrypts it (by reversing the
13+
encryption scheme) to form the original number. [Optional reading project: Research “public key
14+
cryptography” in general and the PGP (Pretty Good Privacy) specific public key scheme. You may
15+
also want to investigate the RSA scheme, which is widely used in industrial-strength applications.]
16+
17+
*/
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package chapter4;
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import java.util.Scanner;
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public class Encryptor {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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System.out.println("Enter a four-digit number: ");
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int initialNumber = input.nextInt();
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if(initialNumber >= 1000 && initialNumber < 10000){
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int firstDigit = initialNumber / 1000;
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firstDigit += 7;
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firstDigit %= 10;
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int secondDigit = initialNumber % 1000 / 100;
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secondDigit += 7;
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secondDigit %= 10;
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int thirdDigit = initialNumber % 100 / 10;
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thirdDigit += 7;
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thirdDigit %= 10;
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int fourthDigit = initialNumber % 10;
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fourthDigit += 7;
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fourthDigit %= 10;
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int encryptedInteger = thirdDigit * 1000 + fourthDigit * 100 + firstDigit * 10 + secondDigit;
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System.out.println("The encrypted number is " + encryptedInteger);
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}
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}
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}

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