1 / 88

Iteration

Iteration. Java looping. Options while do-while for Allow programs to control how many times a statement list is executed. Averaging. Problem Extract a list of positive numbers from standard input and produce their average Numbers are one per line

gbruns
Download Presentation

Iteration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Iteration

  2. Java looping • Options • while • do-while • for • Allow programs to control how many times a statement list is executed

  3. Averaging • Problem • Extract a list of positive numbers from standard input and produce their average • Numbers are one per line • A negative number acts as a sentinel to indicate that there are no more numbers to process • Observations • Cannot supply sufficient code using just assignments and conditional constructs to solve the problem • Don’t how big of a list to process • Need ability to repeat code as needed

  4. Averaging • Problem • Extract a list of positive numbers from standard input and produce their average • Numbers are one per line • A negative number acts as a sentinel to indicate that there are no more numbers to process • Algorithm • Prepare for processing • Get first input • While there is an input to process do { • Process current input • Get the next input • } • Perform final processing NumberAverage.java

  5. While syntax and semantics

  6. While semantics for averaging problem

  7. Averaging • Problem • Extract a list of positive numbers from standard input and produce their average • Numbers are one per line • A negative number acts as a sentinel to indicate that there are no more numbers to process • Sample run Enter positive numbers one per line. Indicate end of list with a negative number. 4.5 0.5 1.3 -1 Average 2.1

  8. While Semantics

  9. Suppose input contains: 4.5 0.5 -1 Execution Trace int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } Service.java

  10. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); }

  11. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 0

  12. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 0 value 4.5

  13. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 0 value 4.5

  14. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 0 4.5 value 4.5

  15. Suppose input contains: 4.5 0.5 -1 Execution Trace valuesProcessed 0 1 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 4.5 value 4.5

  16. Suppose input contains: 4.50.5 -1 Execution Trace valuesProcessed 1 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 4.5 value 4.5 0.5

  17. Suppose input contains: 4.50.5 -1 Execution Trace valuesProcessed 1 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 4.5 value 0.5

  18. Suppose input contains: 4.50.5 -1 Execution Trace valuesProcessed 1 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 4.5 5.0 value 0.5

  19. Suppose input contains: 4.50.5 -1 Execution Trace valuesProcessed 1 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value 0.5

  20. Suppose input contains: 4.50.5-1 Execution Trace valuesProcessed 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value 1.3 -1

  21. Suppose input contains: 4.50.5-1 Execution Trace valuesProcessed 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value -1

  22. Suppose input contains: 4.50.5-1 Execution Trace valuesProcessed 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value -1

  23. Suppose input contains: 4.50.5-1 Execution Trace valuesProcessed 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value -1 average 2.5

  24. Suppose input contains: 4.50.51.3-1 Execution Trace valuesProcessed 2 int valuesProcessed = 0; double valueSum = 0; double value = stdin.nextDouble()); while (value >= 0) { valueSum += value; ++valuesProcessed; value = stdin.nextDouble()); } if (valuesProcessed > 0) { double average = valueSum / valuesProcessed; System.out.println("Average: " + average); } else { System.out.println("No list to average"); } valueSum 5.0 value -1 average 2.5

  25. Loop design • Questions to consider in loop design and analysis • What initialization is necessary for the loop’s test expression? • What initialization is necessary for the loop’s processing? • What causes the loop to terminate? • What actions should the loop perform? • What actions are necessary to prepare for the next iteration of the loop? • What conditions are true and what conditions are false when the loop is terminated? • When the loop completes what actions are need to prepare for subsequent program processing?

  26. Sentinel • For some input data sets there is no reasonable sentinel value • Examples • Process a series of arbitrary numbers • Processing lines of arbitrary text • What can we do? • Use Scanner methods and an operating system sentinel • hasNext() • hasNextInt() • ... • We will only use hasNext() • MSDOS sentinel Unix sentinel MAC sentinel • CTRL-Z CTRL-D ?

  27. Reading a file • Background

  28. Reading a file • Class File • Provides a system-independent way of representing a file name • Constructor File(String s) • Creates a File with name s • Name can be either an absolute pathname or a pathname relative to the current working folder

  29. Echoing a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close();

  30. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Set up standard input stream

  31. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Determine file name

  32. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Determine the associated file

  33. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Set up file stream

  34. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Process lines one by one

  35. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Is there any text

  36. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Get the next line of text

  37. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Display current line

  38. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Make sure there is another to process If not, loop is done

  39. Reading a file Scanner stdin = Scanner.create(System.in); System.out.print("Filename: "); String filename = stdin.next(); File file = new File(filename); Scanner fileIn = Scanner.create(file); while (fileIn.hasNext()) { String currentLine = fileIn.nextLine(); System.out.println(currentLine); } fileIn.close(); Close the stream

  40. The For Statement

  41. The For Statement

  42. The For Statement

  43. The For Statement

  44. The For Statement

  45. For statement syntax

  46. Execution Trace for (int i = 0; i < 3; ++i) { System.out.println("i is " + i); } System.out.println("all done"); i 0

  47. Execution Trace for (int i = 0; i < 3; ++i) { System.out.println("i is " + i); } System.out.println("all done"); i 0

  48. Execution Trace for (int i = 0; i < 3; ++i) { System.out.println("i is " + i); } System.out.println("all done"); i is 0 i 0

  49. Execution Trace for (int i = 0; i < 3; ++i) { System.out.println(“i is " + i); } System.out.println(“all done"); i is 0 i 0

More Related