Thread: Help with code.

Hi DanyaMartchenkov, welcome to the forums!

I have added "code" tags to your post. Basically you put [code] at the start of a section of code and [/code] at the end: that way the code will be properly formatted by the forum software.

Which is line 11?

Thanks, line 11 is 'add[i] = addend.nextDouble();'

OK. And can you confirm the exact runtime message? Copy and post it.

Exception in thread "main" java.lang.NullPointerException
at Calc.main(Calc.java:11)

That's truly weird! When I run your code I get

3
5
6
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
	at Calc.main(Calc.java:11)

where 3,5,6 were some random input I typed.

To be honest, that's the error I would expect. But let's pursue your NullPointerException...

The error means that somewhere on line 11 you are using a variable as if it had a non null value when it is really null. There are only two candidates: add and addend. (That's because you can't get elements from a null array, or call methods of a null thing.) You can see which of these variables is the problem by printing their values just before line 11.

for (blat = 1; blat != 0; i++) {
    Scanner addend = new Scanner(System.in);
    System.out.println("About to assign the next double to add[i]");
    System.out.println("add=" + add);
    System.out.println("addend=" + addend);
    add[i] = addend.nextDouble();
    blat = addend.nextInt();
}

What is the output with that change? (including your input, if any).

About to assign the next double to add[i]
add=null
addend=java.util.Scanner[delimiters=\p{javaWhitespace}+][position=0][match valid=false][need input=false][source closed=false][skipped=false][group separator=\,][decimal separator=\.][positive prefix=][negative prefix=\Q-\E][positive suffix=][negative suffix=][NaN string=\Q?\E][infinity string=\Q?\E]


Exception in thread "main" java.lang.NullPointerException
at Calc.main(Calc.java:14)

Line 14 is:

add[i] = addend.nextDouble();

--- Update ---

changing

double add[] = {0}

to

double[] add = new double[100];

seemed to fix the error but it still doesn't compile like expected.

The output is indicating that the add array is null. However we can see you assign to it right at the start of main().

I'm bewildered. I was going to suggest that you recompile to make sure you are using exactly the code you posted (ie delete Calc.class and recompile), but the fact that you see the output saying "add=null" means that the program is uptodate. Do double check that your code is exactly what you posted. Consider doing what I did and copying the code from your post and replacing your existing code with that.

Otherwise I am baffled - maybe someone else has a clever idea.

Haha, well, thanks anyways!

Our posts crossed.

If there's a compiler message, post it and the offending code.

I changed it up a bit:

import java.util.Scanner;
 
public class Calc {
	public static void main(String pizdets[]) {
 
		double[] add = new double[100];
		double total = 0;
		int i = 0;
		String svalota = "";
 
		for (i = 0; svalota.equals("=") == false; i++) {
			Scanner addend = new Scanner(System.in);
			add[i] = addend.nextDouble();
			svalota = addend.nextLine();
		}
		for (i = 0; i < add.length; i++) {
			total += add[i];
		}
		System.out.print(total);
	}
}

Now, after sending "=" I get this error message:

Exception in thread "main" java.util.InputMismatchException
	at java.util.Scanner.throwFor(Unknown Source)
	at java.util.Scanner.next(Unknown Source)
	at java.util.Scanner.nextDouble(Unknown Source)
	at Calc.main(Calc.java:13)

--- Update ---

Line 13 being

add[i] = addend.nextDouble();

InputMismatchException means that the stream is looking at the wrong kind of input. It is a runtime error (not a compiler message) and it is occurring when you call nextDouble().

Basically you enter "=", the runtime tries to read that as a double, and you get the exception.

You may have noticed that your code *never* stops and waits for you to enter a value for svalota. This becomes even clearer if you print some prompts:

for (i = 0; svalota.equals("=") == false; i++) {
    Scanner addend = new Scanner(System.in);
    System.out.print("Enter a double: ");
    add[i] = addend.nextDouble();
    System.out.print("Enter svalota");
    svalota = addend.nextLine();
}

And the reason for that is that nextDouble() returns a double but does not move to the next line. So nextLine() will always return straight away and assign an empty string to svalota. It will do this every time. The answer is to read a new line after nextDouble(). You don't do anything with what is read (it is an empty string) but it "positions" the stream properly:

import java.util.Scanner;
 
public class Calc {
    public static void main(String pizdets[]) {
 
        double[] add = new double[100];
        double total = 0;
        int i = 0;
        String svalota = "";
 
        for (i = 0; svalota.equals("=") == false; i++) {
            Scanner addend = new Scanner(System.in);
            add[i] = addend.nextDouble(); // read the double
            addend.nextLine();  // throw away the newline
            svalota = addend.nextLine();  // read = to stop, or something else to continue
        }
        for (i = 0; i < add.length; i++) {
            total += add[i];
        }
        System.out.print(total);
    }
}