macOS Number doubling program

soccersquirt82 said:

I tried to only have one variable, but then the answer is the same as what I put in. Here is the code:

Code:

package numberdoub;
import java.util.*;
public class Numberdoub
{
	static double redouble (double x){
		
		//rd method
		while (x < 1000){
		x = 2*x;}
		return x;
	}
	
	public static void main(String[] args) {
		
		//defines variable
		double x;
		
		Scanner sc = new Scanner (System.in);
		
		//user input
		System.out.print("x = ");
		x = sc.nextDouble();

		//answers
		System.out.println("The answer is: " + x);		
	}
}[/QUOTE]

redouble looks great. Now you need to use it. You never call redouble. Just because you called the variable in redouble x, and you have an x in main, doesn't mean they are the same variable. You will need to call redouble from main, and pass it main's x. What it returns will be your answer, so you'll need to do something with it.

-Lee

Click to expand...

soccersquirt82 said:

I think I used redouble in the right way. The answer is still the same, though.

Code:

package numberdoub;
import java.util.*;
public class Numberdoub
{
	static double redouble (double x){
		
		//rd method
		while (x < 1000){
		x = 2*x;}
		return x;
	}
	
	public static void main(String[] args) {
		
		double redouble = 0;
		double x;
		
		Scanner sc = new Scanner (System.in);
		
		//user input
		System.out.print("x = ");
		redouble = sc.nextDouble();

		//answers
		System.out.println("The answer is: " + x);		
	}
}[/QUOTE]

I know for sure we went over this before. =)
You don't need to declare the type of functions in java. this is not fortran.
You were assigning sc.nextDouble() to x. That was good. You then need to call the function redouble on x, and do something with its result. Calling a function that returns a value looks like:
[CODE]double myResult = myDoubleFunction(myArgument);

-Lee

Click to expand...

soccersquirt82 said:

Like this?

Code:

package numberdoub;
import java.util.*;
public class Numberdoub
{
	static double redouble (double x){
		
		//rd method
		while (x < 1000){
		x = 2*x;}
		return x;
	}
	
	public static void main(String[] args) {
		
		double redouble = 0;
		double x;
						
		Scanner sc = new Scanner (System.in);
		
		//user input
		System.out.print("x = ");
		redouble = sc.nextDouble();

		x = redouble(x);
		
		//answers
		System.out.println("The answer is: " + redouble(x));		
	}
}[/QUOTE]

Very nearly. For one, get rid of double redouble = 0;
Next, you need to assign the value from your Scanner to what you're going to pass to redouble.
Lastly, you only need to call redouble on x once. Now you're doing it, and assigning the result to x (so x has the result from redouble in it), then you're calling it again in your print statement. You can do it in one or the other. In this case it won't matter, because calling redouble on something over 1000 should result in the same value as you passed in, in general you want to call a function like this only once.

-Lee

Click to expand...

soccersquirt82 said:

IT WORKS!!!! YAY!! Thanks so much. Just one more to go!

Code:

package numberdoub;
import java.util.*;
public class Numberdoub
{
	static double redouble (double x){
		
		//rd method
		while (x < 1000){
		x = 2*x;}
		return x;
	}
	
	public static void main(String[] args) {
		
		double x;
						
		Scanner sc = new Scanner (System.in);
		
		//user input
		System.out.print("x = ");
		x = sc.nextDouble();

		//answers
		System.out.println("The answer is: " + redouble(x));		
	}
}[/QUOTE]

Great! =)
One tip, though... what if x is entered as -2? I am not sure if you're supposed to consider this, but in reality it is very important, as no matter how many times you double a negative number, it will never get over 1000 (unless there is an overflow, but i believe java will die with an exception instead of overflowing).

There is a Math.abs() function that will give you the absolute value, otherwise it's pretty easy to fake yourself.

-Lee

Edit: I was wrong, even for integers Java allows for +/-Infinity. So this will lead to an infinite loop instead of a crash condition, which is probably worse depending on who you ask.

Click to expand...

soccersquirt82 said:

That would make the answer 0 which isn't what I want.

Click to expand...