No login screen appears when starting Windows XP computer

Question

I want to implement a Repeat Until in Scala.

The commented code will throw a StackOverflowException.

But the code now run in main method works.

But I don't know why and what's the difference between these two snippets.

object REPEAT{
    class REPEAT(command: => Unit){
        def UNTIL(cond: => Boolean):Unit = {
            command
            if(!cond) UNTIL(cond)
        }
    }

    def REPEAT(command: => Unit): REPEAT = {
        new REPEAT(command)
    }

    def main(args: Array[String]) {
        /* this code work well */
        var i = 0
        REPEAT { i+= 1; println(i)} UNTIL (i == 100)

        /*
        // something wrong in this code.
        var i = 0
        new REPEAT {
            i += 1; println(i)
        } UNTIL (i == 100)
        */          
    }
}

ps: I found the wrong code just change the var i to 1 but don't change it anymore.

The wrong code's output:

1

Exception in thread "main" java.lang.StackOverflowError at REPEAT$$anon$1$$anonfun$$lessinit$greater$1.apply$mcV$sp(REPEAT.scala:15) at REPEAT$REPEAT.UNTIL(REPEAT.scala:4)

Solution

Can you boot from a rescue CD such as Ultimate Boot for Windows? UBCD From there I would recommend running chkdsk /r to see if there is a file system issue. You can also scan for malware offline. It may be: bad disk, malware or a corrupt profile. Good Luck

Comments

[Vlueboy]

You still have to try the "last known good configuration" option (press F8 a LOT after the BIOS POST and before the "Windows XP" screen comes up). Also whether it is a dual-monitor desktop where your one monitor is showing the right, empty half of your desktop, and plug in the correct one --you'll know it if you move the mouse to the left border of the screen and it does not appear to stop.

[Jonas]

@Vlueboy: I tried that alternative now, but I got the same problem: just seeing the background and can move the mouse around.

[Vlueboy]

Thanks @Jonas. Which one, the first one about Last Known good? It isn't effective when the problem is old. How old is it? What happened with my monitor-card check? are you sure you're not seeing what desktop #2 shows rather than desktop #1? it's the only other thing short of a reinstall I can think of.

[Jonas]

@Vlueboy: The computer, only has one monitor. We got this problem last friday.

[Vlueboy]

on further thought I meant "dual-head" instead of dual-monitor;some PCs have multiple output "heads" so Windows may be trying to display the login screen's half through the other outlet --if you have overlooked it and someone changed display settings on friday. When you move your mouse in straight lines around the screen borders, it must NOT exit into hidden desktop space. That's a sign of the problem I mentioned. Otherwise, keep googling 'missing "domain login screen" ' or try a repair install, lastly

[dk14]

it doesn't compile if uncomment your commented code (var i defined twice). WIthout it - prints 1 to 100 as expected. If you write REPEAT { i+= 1; println(i)} UNTIL (i == 100) twice - it will cause the stackoverflow as it will start from i=101 and end at i=infinity.

[sjrd]

As it stands, I am pretty sure your UNTIL method is not tail-recursive, because it is neither private nor final. With longer loops you'll get a StackOverflow as well. You should add the @tailrec annotation to that method.

[VoidBzY]

I am sorry I didn't express it clearly. The code which run in the main method is to replace the code commented.