1 / 18

Understanding Looping in Java Programming

This guide covers various looping techniques in Java programming, including while, do-while, and for loops, with examples and flow charts. Learn how to use break and continue keywords effectively.

pangle
Download Presentation

Understanding Looping in Java Programming

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. Selection Statements • Using if and if...else • Nested if Statements • Using switch Statements • Conditional Operator • Repetition Statements • Looping: while, do-while,and for • Nested loops • Using break and continue Chapter 3 Control Statements

  2. Repetitions • while Loops • do-while Loops • for Loops • break and continue

  3. while Loop Flow Chart while (continuation-condition) { // loop-body; }

  4. while Loop Flow Chart, cont. int i = 0; while (i < 100) { System.out.println( "Welcome to Java!"); i++; }

  5. Example 3.2: Using while Loops // TestWhile.java: Test the while loop import javax.swing.JOptionPane; public class TestWhile { /** Main method */ public static void main(String[] args) { int data; int sum = 0; // Read an initial data String dataString = JOptionPane.showInputDialog(null, "Enter an int value, \nthe program exits if the input is 0", "Example 3.2 Input", JOptionPane.QUESTION_MESSAGE); data = Integer.parseInt(dataString); // Keep reading data until the input is 0 while (data != 0) { sum += data; // Read the next data dataString = JOptionPane.showInputDialog(null, "Enter an int value, \nthe program exits if the input is 0", "Example 3.2 Input", JOptionPane.QUESTION_MESSAGE); data = Integer.parseInt(dataString); } JOptionPane.showMessageDialog(null, "The sum is " + sum, "Example 3.2 Output", JOptionPane.INFORMATION_MESSAGE); System.exit(0); } }

  6. Caution Don’t use floating-point values for equality checking in a loop control. Since floating-point values are approximations, using them could result in imprecise counter values and inaccurate results. This example uses int value for data. If a floating-point type value is used for data, (data != 0) may be true even though data is 0. // data should be zero double data = Math.pow(Math.sqrt(2), 2) - 2; if (data == 0) System.out.println("data is zero"); else System.out.println("data is not zero");

  7. do-while Loop do { // Loop body; } while (continue-condition);

  8. for Loops for (initial-action; loop-continuation-condition; action-after-each-iteration) { //loop body; } int i = 0; while (i < 100) { System.out.println("Welcome to Java! ” + i); i++; } Example: int i; for (i = 0; i < 100; i++) { System.out.println("Welcome to Java! ” + i); }

  9. for Loop Flow Chart for (initial-action; loop-continuation-condition; action-after-each-iteration) { //loop body; }

  10. for Loop Example int i; for (i = 0; i<100; i++) { System.out.println( "Welcome to Java"); }

  11. Which Loop to Use? The three forms of loop statements, while, do, and for, are expressively equivalent; that is, you can write a loop in any of these three forms. I recommend that you use the one that is most intuitive and comfortable for you. In general, a for loop may be used if the number of repetitions is known, as, for example, when you need to print a message 100 times. A while loop may be used if the number of repetitions is not known, as in the case of reading the numbers until the input is 0. A do-while loop can be used to replace a while loop if the loop body has to be executed before testing the continuation condition.

  12. Caution Adding a semicolon at the end of the for clause before the loop body is a common mistake, as shown below: for (int i=0; i<10; i++); { System.out.println("i is " + i); } Wrong

  13. Caution, cont. Wrong Similarly, the following loop is also wrong: int i=0; while (i<10); { System.out.println("i is " + i); i++; } In the case of the do loop, the following semicolon is needed to end the loop. int i=0; do { System.out.println("i is " + i); i++; } while (i<10); Correct

  14. The break Keyword

  15. The continue Keyword

  16. Using break Example for using the break keyword: 3.5 // TestBreak.java: Test the break keyword in the loop public class TestBreak { /** Main method */ public static void main(String[] args) { int sum = 0; int item = 0; while (item < 5) { item ++; sum += item; //if (sum >= 6) break; } System.out.println("The sum is " + sum); } }

  17. Using continue Example for using the continue keyword: // TestContinue.java: Test the continue keyword public class TestContinue { /** Main method */ public static void main(String[] args) { int sum = 0; int item = 0; while (item < 5) { item++; if (item == 2) continue; sum += item; } System.out.println("The sum is " + sum); } }

  18. Review of Terms: Deena’s Class • The 3 essential elements of a programming loop: priming, test, and update • User-controlled loops vs Program-controlled loops • Some user-controlled loops use sentinels. • Accumulator and Marker variables: how are these used in loops? • What is a flag variable? When do you use it?

More Related