Array Out Of Bounds Error - but why?

If I take your formatNumber and use this to run it, the problem I see is that the null causes a problem (it can't be rounded or converted to a number.)

        
        var d=[1028, 1, 7, 13.980000, 200, 58, null];       
    	for(var i=0;i<d.size();i++) {
			System.println("try "+d[i]);
			System.println("ret="+formatNumber(d[i])); 
			System.println("ba="+gAccum5);   	
    	}

I suspect your problem is how/when you are calling formatNumber() or what you do with gAccm5 outside of the code you posted

You can catch the null with this as the first line in formatNumber()

if(n==null) {return 0;}

Try adding this to the beginning of formatNumber() It may help you see what's going on

System.println("ba="+gAccum5);

Solved - thanks jim_m_58 for help.
Error reason: I know about null problem but I filter out null value outside the function just before calling (because I need different action if the parameter is null). But the idea "what you do with gAccum5 outside the code" was the hint. In upper level code, for some specific parameter value, I set gAccum5 = ['-','-','-',']; instead of formatNumber() calling which of course shortened the array. Agrrr ... stupid mistake, some mist covered my eyes yesterday. Thanks again.

To protect in the future, you could have the byte array local to formatNumber and return it.

So in formatNumber,

 var ba=[0,0,0,0,0]b;

then

return [ba,idx];

and in the calling code, 

var fmt=formatNumber(n);

gAccum5=fmt[0];

size=fmt[1];

or something like this

I'm kind of wondering what you are using this for, as if you just want to format a number for output, there's an easier way

Say you have

var num=123;

with num.format("%d") you get a string, and if you want a fixed size, num.format("%08d")

based on the string you pass to format(),you can do a number of things.  Like with a float, display a single decimal place

var flt=1.2345;

flt.format("%0.1f")

and you get "1.2" 

I have reopened the code after several months and now I'm wondering too.
If I look at the code in detail, I wanted to convert numbers (always integer between -9999 to 9999) to some array of digits code (I used byte array, I do not know why), then add/insert some specific characters code (degree character to signalize temperature, arrow character to signalize wind speed/direction etc), and than I call function which takes element-by-element from array and draw corresponding bitmap to screen (I do not use font due to aliasing required which is not possible in used dc).

So, if it is possible to read/write string elements by index (str[3]), I can move from byte arrays to strings.

Ok, with a custom font, they can be ani-aliased:

<font id="large" antialias="true"  filename="lai65.fnt"/>

With fonts, you can use setColor() and not need bitmaps for different colors

Say you have

var string= "12345";

you can make it a character array with

var ca=string.toCharArray()

and access a character at a time

The way I do things like a degree symbol is:

var degree="°"; //utf-8, b0 hex, 176 dec

and then just display

temperature+degree (using dc.drawText())