// 10/16/2017

/** more ways of using While loop
 */

import java.util.Scanner;

public class WhileLoopMore {
  /**
   */
  public static void main(String[] args)   {
    
    // example1: we know how many times to execute
    int number=5; // loop will execute 'number' times
    while (number > 0) {
      System.out.println("Hello, number is now: " + number);
      number--;
    } // end of while loop
     
    Scanner in = new Scanner(System.in);
    // example2a: we ask the user whether they want to continue
    String answer="Y";
    //while (answer.charAt(0)=='Y' || answer.charAt(0)=='y') { // continues only if user enters Y
    while (answer.charAt(0)!='N' && answer.charAt(0)!='n')  {
      // this loop will execute as long as the user enters anything
      // other than 'N'
        // play a game...
        System.out.println("playing game...");
        System.out.print("Do you want to continue (Y for yes, N for no): ");        
        answer=in.nextLine();
    }
    // example2b: we ask the user whether they want to continue
    // this one works with a boolean variable
    boolean done=false;
    while (!done)  {
        System.out.println("playing game loop 2...");
        System.out.print("Do you want to continue (Y for yes, N for no): ");        
        answer=in.nextLine();
        //if (!(answer.charAt(0)=='Y' || answer.charAt(0)=='y'))
        //if (answer.charAt(0)!='Y' && answer.charAt(0)!='y')
        if (answer.charAt(0)=='N' || answer.charAt(0)=='n')
          done=true;
    }
    
    // while loop with sentinel 
    System.out.println("entering while loop with sentinel.");
    
    // structured read loop
    int idnum;
    // one read BEFORE enter while loop
    System.out.print("Enter idnum (-1 to exit): ");
    idnum = in.nextInt();
    while (idnum!=-1)  {
      System.out.println("iterating while loop again...");
      // another read at the END of the while loop
      System.out.print("Enter idnum (-1 to exit): ");
      idnum = in.nextInt();
    }
    
    // validate a grade 
    double grade;
    System.out.print("Enter a grade: ");
    grade = in.nextDouble();
    // while the grade is not in range, ask for another input
    //while (grade<1 || grade>100)
    while (! (grade>=1 && grade<=100)) {
         System.out.println("that grade is invalid.");
         System.out.print("Enter a grade: ");
         grade = in.nextDouble();
    }
    // valid, fall out of loop
    
  }
}