CONTROL STRUCTURES II: REPETITION - Java Programming: From Problem Analysis to Program Design - page 264

Example 5-6 further illustrates the use of a flag-controlled while loop.

EXAMPLE 5-6 GUESSING THE NUMBER GAME

The following program randomly generates an integer greater than or equal to 0 and less
than 100 . The program then prompts the user to guess the number. If the user guesses the
number correctly, the program outputs an appropriate message. Otherwise, the program
checks whether the guessed number is less than the random number. If the guessed
number is less than the random the number generated by the program, the program
outputs the message, ''Your guess is lower than the number''; otherwise, the program
outputs the message, ''Your guess is higher than the number''. The program then
prompts the user to enter another number. The user is prompted to guess the random
number until the user enters the correct number.
The program uses the method random of the class Math to generate a random number.
To be specific, the expression:

Math.random()

returns a value of type double greater than or equal to 0.0 and less than 1.0 . To convert
it to an integer greater than or equal to 0 and less than 100 , the program uses the
following expression:
( int ) (Math.random() * 100);

Furthermore, the program uses the boolean variable done to control the loop. The
boolean variable done is initialized to false . It is set to true when the user guesses the
correct number.

//Flag-controlled while loop.
//Guessing the number game.

import java.util.*;
public class FlagControlledLoop
{

static Scanner console = new Scanner(System.in);

public static void main(String[] args)
{

//declare the variables
int num; //variable to store the random number

int guess; //variable to store the number

//guessed by the user

boolean done; //boolean variable to control the loop

num = ( int ) (Math.random() * 100); //Line 1

done = false ; //Line 2

while (!done) //Line 3

{ //Line 4