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Comp102 lec 6


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  • 1. Java in two semesters by Quentin Charatan & Aaron Kans
  • 2.  Computers can repeat the same tasks over and over, again and again Form of program control that allows us to instruct the computer to carry out a task by repeating a section of code  Iteration  Loop Types of Loops  for loop  while loop  do...while loop
  • 3. System.out.println(“*****”);***** System.out.println(“*****”);***** System.out.println(“*****”);***** System.out.println(“*****”);***** System.out.println(“*****”);***** Loop 1…5 System.out.println(“*****”); End-Loop for(int i=0; i<5; i++) { System.out.println(“*****”); }
  • 4. 109 for(int i=10; i>=1; i--)8 {7 System.out.println(i);6 }54321
  • 5. 24 for(int i=1; i<=20;i++)6 {8 if(i%2 ==0)10 {12 System.out.println(i);14 }16 }1820
  • 6. for(int i=0; i<5; i++)***** {***** for(int j = 0; j<5; j++***** {***** System.out.print(“*”); System.out.println(“*”);***** } } System.out.println(); }
  • 7.  Often used to implement the fixed repetitions
  • 8.  Consider the following scenarios  A racing game that repeatedly moves a car around until the car crashes  A ticket issuing program that repeatedly offers tickets for sale until he user chooses to quit the program  A password checking program that does not let a user enter into an application until he or she enters the right password Thenumber of repetitions is not fiexed but depends on some condition  Non fixed Iterations
  • 9. while (/*test goes here*/){ //instruction(s) to be repeated} simpler to construct If not used as counter loop, then it is not required to keep a counter Normally used to validate the input
  • 10. import java.util.Scanner;public class Assignment1{ public static void main(String[] args) { int marks; Scanner input = new Scanner(; marks = input.nextInt(); while(marks<0 || marks>100) { System.out.println("Invalid Marks - ReEnter?"); marks = input.nextInt(); } if(marks>=40) { System.out.println("Congratulations... You passed"); } else { System.out.println("Sorry you failed the course"); } }}
  • 11. int i=0; while(i<5)***** {***** int j = 0;***** while(j<5)***** {***** System.out.print(“*”); j++; } System.out.println(); i++; }
  • 12.  Tests the condition at beginning If the condition is false at start, makes the loop to not execute ever  Loop executes ZERO or MORE times
  • 13.  Non – Fixed Loop Condition is tested at the end of the loop Makes the loop to iterate at least once Makes the loop to iterate ONE or MORE times while loop terminates once the program has done its job.  Do while is suitable if we wish to re-run the same program again based on user response Syntax:do{ //instruction(s) to be repeated goes here}while (/* test goes here*/);
  • 14. char response;do{ Scanner input = new Scanner(; //program instructions go here System.out.println(“Want to re-run? (y/n)”); response =;}while(response ==‘y’);
  • 15. do{ System.out.println("1 - for group A"); System.out.println("2 - for group B"); System.out.println("3 - Quit"); response = sc.nextInt(); switch(response) { case 1: System.out.println("10:00 AM"); break; case 2: System.out.println("11:00 AM"); break; case 3: System.out.println("Good Bye"); break; default: System.out.println("Invalid Input"); break; }}while(response!= 3);
  • 16.  For Loop  Number of repetitions required can be determined prior to entering the loop While Loop  Number of repetitions cannot be determined prior to entering the loop and  Zero repetitions is allowed Do… while loop  Number of repetitions cannot be determined before the loop  You require at least one repetition of loop