Programming Fundamentals I Java Programming Spring 2009

1. Programming Fundamentals IJava Programming Spring 2009 Instructor: Xuan Tung Hoang tung_hx@icu.ac.kr TA: Tran Minh Trung trungtm@icu.ac.kt Lab 03

2. Content • Multiplication test • Duplicate elimination • Homework #3

3. Exercise 1: Multiplication test • Write a program to check the capability of user to perform simple multiplication as following • Use a Random object to produce two positive one-digit integers. The program should then prompt the user with a question, such as • How much is 6 times 7? • The user then inputs the answer. • The program checks the user’s answer. • If it is correct • Display the message "Very good!" • Ask another multiplication question • If the answer is wrong • Display the message "No. Please try again." • Let the student try the same question repeatedly until the student finally gets it right. • A separate method should be used to generate each new question. This method should be called once when the application begins execution and each time the user answers the question correctly.

4. Exercise 1: Template (1) // Multiply.java // Program generates single digit multiplication problems import java.util.*; public class Multiply { Random randomNumbers = newRandom(); int answer; // the correct answer // ask the user to answer multiplication problems public void quiz() { Scanner input = newScanner( System.in ); int guess; // the user's guess /* write code to call method createQuestion to display the question */ System.out.println( "Enter your answer (-1 to exit):" ); guess = input.nextInt(); while ( guess != -1 ) { /* write code to call the method checkResponse to check the user’s answer */ System.out.println( "Enter your answer (-1 to exit):" ); guess = input.nextInt(); } // end while } // end method /* write code for the createQuestion, checkResponse method (next slide)*/ } // end class Multiply

5. Exercise 1: Template (2) //createQuestion method: prints a new question and stores the corresponding answer /* write method header for the createQuestion method */ { // get two random numbers between 0 and 9 /* Write code to get two random numbers and store them in variables digit1 and digit2. */ /* Write code to multiply the two variables and store the result in variable answer */ System.out.printf( "How much is %d times %d?\n", digit1, digit2 ); } // end method createQuestion //checkResponse method: checks if the user answered correctly /* Write method header for checkResponse */ { /* Write code to test whether the answer is incorrect */ /* Write code to tell the user to try again, if the answer is incorrect */ else { System.out.println( "Very Good!" ); /* Write code to call method createQuestion to display another question */ } // end else } // end method checkResponse Q: How to generate random integers from 0 to n-1 ?: A: Google with key words: “random + java tutorial”

6. Exercise 1: Sample output How much is 0 times 8? Enter your answer (-1 to exit): 0 Very Good! How much is 3 times 9? Enter your answer (-1 to exit): 21 No. Please try again. Enter your answer (-1 to exit): 27 Very Good! How much is 8 times 1? Enter your answer (-1 to exit): -1

7. Exercise 2: Duplicate elimination • Write an application that inputs five numbers, each between 10 and 100. • Display an input number only if it is not a duplicate of a number already read. • Display the complete set of unique values input after the user inputs each new value. • Use the smallest possible array to solve this problem.

8. Exercise 2: Template (1) // Unique.java // Reads in 5 unique numbers. import java.util.Scanner; publicclass Unique { // gets 5 unique numbers from the user publicvoid getNumbers() { Scanner input = newScanner( System.in ); /* Create an array of five elements*/ int count = 0; // number of uniques read int entered = 0; // number of entered numbers while( entered < numbers.length ) { System.out.print( "Enter number: " ); /* Write code here to retrieve the input from the user */ // validate the input (next slide) /* Write an if statement that validates the input */ // print the list of unique values /* Write code to output the contents of the array */ } // end while } // end method getNumbers } // end class Unique

9. Exercise 2: Template (2) // validate the input if (//*add validate condition) { // flags whether this number already exists boolean containsNumber = false; // increment number of entered numbers entered++; /* Compare the user input to the unique numbers in the array using a for statement. If the number is unique, store new number */ /* add the user input to the array only if the number is not already in the array */ if ( !containsNumber ) { /* Write code to add the number to the array and increment unique items input */ } // end if else System.out.printf( "%d has already been entered\n“, number ); } // end if else System.out.println( "number must be between 10 and 100" );

10. Exercise 2: 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 11 85 26 Enter number: 41 11 85 26 41 Enter number: 99 11 85 26 41 99

11. Homework #3

12. Submission and Report • Due: 1th April, mid-night • Compress your source/class files into a ZIP file • Name the zip file according with the following template: • StudentID_labNumber.zip • Example: 20091004_lab1.zip • Submit the file to TA • Email address: submit.hw.code@gmail.com • Subject: “StudentID_ICE0124_lab1” • Example: 20061004_ICE0124_lab1