1. Zhen Jiang Dept. of Computer Science West Chester University West Chester, PA 19383 zjiang@wcupa.edu CSC141 Computer Science I 2/4/20161

2. Price is right. Sample execution (click on this link to try)this link http://www.cis.temple.edu/~jiang/price_is_right.exe Each button in the above sample REPEAT …? Loop 2/4/20162

3. While loop Format & Logic, page 197, Figure 4-1. Sample, code 4-3, page 198. 2/4/20163

4. 4 ; while ( ) { ; }

5. Do-while loop Format, page 208 Logic, page 209, Figure 4-6. Sample, code 4-6, page 209. 2/4/20165

6. 6 How does this differ from the while loop? The controlled will always execute the first time, regardless of whether the is true or false. 2/4/2016

7. For loop Format, page 212, Figure 4-7. Logic, page 212, Figure 4-8. Sample, code 4-7, page 213. 2/4/20167

8. 8 for ( ; ; ) { ; } 2/4/2016

9. 9 Summary Body first, and then event change/update

10. Development process http://www.cis.temple.edu/~jiang/LoopDevelopment.htm 2/4/201610

11. 2/4/201611

12. Controlling Number of Loop Iterations If the number of iterations is known before the loop starts, the loop is called a count- controlled loop. Counter =0, counter++, counter <number Counter = 1, counter++, counter <=number Use for loop for an easy development. 2/4/201612

13. 2/4/201613

14. 2/4/201614

15. 15 Code: for (int i = 1; i <= 4; i++) { System.out.println(i + " squared is " + (i * i)); } Output: 1 squared is 1 2 squared is 4 3 squared is 9 4 squared is 16 2/4/2016

16. 16 Code: n=keyboard.nextInt(); // try 6! for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { System.out.print("*"); } System.out.println(); } Output: ****** 2/4/2016

17. 17 Code: n=keyboard.nextInt(); // try 5! for (int i = 1; i <= n; i++) { for (int j = 1; j <= 10; j++) { System.out.print((i * j) + " "); } System.out.println(); } Output: 1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 12 14 16 18 20 3 6 9 12 15 18 21 24 27 30 4 8 12 16 20 24 28 32 36 40 5 10 15 20 25 30 35 40 45 50 2/4/2016

18. 18 Code: n=keyboard.nextInt(); // try 6! for (i = 1; i<=n; i++) System.out.print(“*”); System.out.println(“”); for (i = 1; i <= n-2; i++) { System.out.print(“*”); for (int j = 1; j <= n-2; j++) System.out.print(“ ”); System.out.println(“*”); } for (i = 1; i<=n; i++) System.out.print(“*”); System.out.println(“”); Output: ****** * ****** 2/4/2016

19. 19 Code: n=keyboard.nextInt(); // try 6! for (int i = 1; i <= n; i++) { for (int j = 1; j <= i; j++) { System.out.print("*"); } System.out.println(); } Output: * ** *** **** ***** ****** 2/4/2016

20. 20 Code: n=keyboard.nextInt(); // try 6! for (int i = 1; i <= n; i++) { for (int j = 1; j <= i; j++) { System.out.print(i); } System.out.println(); } Output: 1 22 333 4444 55555 666666 2/4/2016

21. 21 Code: n=keyboard.nextInt(); // try 5! for (int i = 1; i <= n; i++) { for (int j = 1; j <= (n - i); j++) { System.out.print(" "); } for (int k = 1; k <= i; k++) { System.out.print(i); } System.out.println(); } Output: 1 22 333 4444 55555 2/4/2016

22. Otherwise (unknown or unclear), the loop is called a event-controlled loop. Use a while loop or a do-while loop for an easy checkpoint development. Asking the user before each iteration if it is time to end the loop is called the ask-before-iterating technique. Appropriate status update (or event initializing) for a sequence of iterations 2/4/201622 Controlling Event of Loop Iterations

23. 2/4/201623

24. 24 Finds and prints a number's first factor other than 1: int n = keyboard.nextInt(); // try 91 int f = 2; while (n % f != 0) { f++; } System.out.println("First factor:" + f); Sample run: First factor:7 2/4/2016

25. 25 Write a program that will repeatedly prompt the user to type a number until the user types a non-negative number, then square it. Example log: Type a non-negative integer: -5 Invalid number, try again: -1 Invalid number, try again: -235 Invalid number, try again: -87 Invalid number, try again: 11 11 squared is 121 2/4/2016

26. 26 System.out.print("Type a non-negative integer: "); int n = keyboard.nextInt(); while (n < 0) { System.out.print("Invalid number, try again: "); n = keyboard.nextInt(); } int square = n * n; System.out.println(n + " squared is " + square); Notice that the number variable had to be declared outside the while loop in order to remain in scope. 2/4/2016

27. 27 Write a class named DigitSum that reads an integer from the user and prints the sum of the digits of that number. You may assume that the number is non-negative. Example: Enter a nonnegative number: 29107 prints out 19 (i.e., 2+9+1+0+7 ) Hint: Use the % operator to extract the last digit of a number. If we do this repeatedly, when should we stop? 2/4/2016

28. 28 import java.util.Scanner; public class DigitSum { public static void main(String [] args) { Scanner keyboard = new Scanner(System.in); int n = keyboard.nextInt(); int sum = 0; while (n > 0) { sum += n % 10; // add last digit to sum n = n / 10; // remove last digit } System.out.println(“sum = “ + sum); } } 2/4/2016

29. 29 Write a program named CountFactors that reads in an integer and displays its number of factors. For example, if the user enters 60, CountFactors displays 12 because 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60 are all factors of 60. Scanner keyboard = new Scanner(System.in); int n = keyboard.nextInt(); int sum = 0, k = ?; while ( ) { } System.out.println(“sum = “ + sum); 2/4/2016

30. Exercise population http://www.cis.temple.edu/~jiang/6billion.exe TV purchase http://www.cis.temple.edu/~jiang/tv563.exe 1+2+4+8+... http://www.cis.temple.edu/~jiang/1_2_4.exe 1+2+3+4+...+99 1+2+3+4+...+99 http://www.cis.temple.edu/~jiang/1to99.exe 2/4/201630

31. 2/4/201631

32. Solution 2/4/201632

33. File writing, page 237-240 Filename PringWriter Println Close Sample, code 4-17, page 237 2/4/201633

34. Appending data to a (existing) file FileWriter (, true), page 240 2/4/201634

35. File Reading, page 241-245 File Scanner nextXXXX( ) close Sample, code 4-18, page 242. 2/4/201635

36. Detecting the end of a file hasNext Code 4-19, page 245. Detecting the existence of a file exists Code 4-21, page 249. 2/4/201636

37. Random number generator randomNumbers.nextXXX( ) Sample, code 4-23, page 253. 2/4/201637

38. 38 Objects of the Random class generate pseudo-random numbers. Class Random is found in the java.util package. import java.util.*; The methods of a Random object returns a random real number in the range [0.0, 1.0)‏ nextDouble()‏ returns a random integer in the range [0, max)‏ in other words, from 0 to one less than max nextInt( max )‏ returns a random integer nextInt()‏ DescriptionMethod name 2/4/2016