Need help with my while loops please do not know what I'm doing wrong

[ndsmith20]

I am having a couple issue with my while loops...I cannot exit my first while loop even when I enter the correct information and if i cancel out the entire first while loop I escape the second loop no matter what after my second entry...here is just the test portion of my code:

import java.util.*;

public class TestSailBoat
{
	public static void main(String[] args)
	{
		//Attributs
		int _numSails;
		int _lengthBoat;
		String _colour;
		
		//allows user to enter information about the boat
		Scanner scanner = new Scanner(System.in);
		System.out.print("Colour of boat: ");
		_colour = scanner.nextLine();
		while((!_colour.equals("red"))||(!_colour.equals("blue"))||(!_colour.equals("white"))||(!_colour.equals("yellow")))
			{
				System.out.println("ERROR: color must be red, white, blue or yellow");
				System.out.print("Colour of boat: ");
				_colour = scanner.nextLine();
			}
		System.out.print("Lenght of boat: ");
		_lengthBoat = Integer.parseInt(scanner.nextLine());
		while ((_lengthBoat < 0) && (_lengthBoat > 50));
			{
				System.out.println("ERROR: length of boat must be between 0 and 50 inclusively");
				System.out.print("Lenght of boat: ");
				_lengthBoat = Integer.parseInt(scanner.nextLine());
			}
		System.out.print("Number of sails: ");
		_numSails = Integer.parseInt(scanner.nextLine());
		while (_numSails < 1 && _numSails > 4)
			{
				System.out.println("ERROR: number of sails must be between 1 and 4 inclusively");
				System.out.print("Number of sails: ");
				_numSails = Integer.parseInt(scanner.nextLine());
			}
		SailBoat sails = new SailBoat(_colour, _lengthBoat, _numSails);
		sails.calcPrice();
		System.out.println(sails.toString());
	}
}

Results:
First Loop:
Colour of boat: red
ERROR: color must be red, white, blue or yellow
Colour of boat: white
ERROR: color must be red, white, blue or yellow
Colour of boat: blue
ERROR: color must be red, white, blue or yellow
Colour of boat:

Second Loop:
Colour of boat: white
Lenght of boat: 98
ERROR: length of boat must be between 0 and 50 inclusively
Lenght of boat: 98
Number of sails:

I have not even tried testing the third loop yet

[wsaryada]

You are using the wrong operator there. When you are using the || operator when one expression is true then the result will be true.

                colors
                -------------------------
                !r    !w    !b    !y
inputs
    red          F     T     T     T  = T
    white        T     F     F     F  = T       
    blue         T     T     F     T  = T
    yellow       T     T     T     F  = T

Your other while loop also have a wrong expression, where the condition will never be true. No number is less and greater than something at the same time.

[ndsmith20]

Thank you wsaryada. I updated the second and third while loops in my code to be || instead of &&. That issue seems to be resolved now. I do not understand what type of operator I should use for the colors. I though it would be or (||) but your reasoning definitely makes sense (taking discrete math currently). What would you recommend?

[JosAH]

De Morgan already solved this small problem in the 19th century: if you want the colour to be one of red, white, blue or yellow, we can write it down an red || white || blue || yellow. If the colour isn't one of those colours, the expression !(red || white || blue || yellow) is true; De Morgan figured out that the last expression is equivalent to !red && !white && !blue && !yellow.

kind regards,

Jos

[ndsmith20]

thank you so much JosAH that worked for the colors and now for some reason the lengthBoat loop is not working:

System.out.print("Lenght of boat: ");
		_lengthBoat = Integer.parseInt(scanner.nextLine());
		while (_lengthBoat < 0 || _lengthBoat > 50);
			{
				System.out.println("ERROR: length of boat must be between 0 and 50 inclusively");
				System.out.print("Lenght of boat: ");
				_lengthBoat = Integer.parseInt(scanner.nextLine());
			}
		System.out.print("Size of engine: ");
		_sizeOfEngine = Integer.parseInt(scanner.nextLine());
		while (_sizeOfEngine < 1 || _sizeOfEngine > 350)
			{
				System.out.println("ERROR: size of engine must be between 1 and 350 inclusively");
				System.out.print("Size of engine: ");
				_sizeOfEngine = Integer.parseInt(scanner.nextLine());
			}

my input:
Colour of boat: red
Lenght of boat: 34
ERROR: length of boat must be between 0 and 50 inclusively
Lenght of boat: 65
Number of sails:

[JosAH]

		while (_lengthBoat < 0 || _lengthBoat > 50);

What's that semi colon doing there? (it's an empty statement).

kind regards,

Jos

[ndsmith20]

Thank you, that fixed it Jos. It is so strange how you miss the little things when looking at your own code. :)