Doubt In Kathy& Bates book questions at page 198

[vatsalya rao]

The questions are as follows:

Class test{
public static void main(String arg[])
{
int x=0,y=0;
for(int z=0;z<5;z++)
{
if((++x>2)||(++y>2))
{
x++;
}
}
System.out.println(x + " " +y);
}

}

I traced it as follows

z=0- x=1,y=1;
z=1 x=2,y=2;
z=3 x=3 ,y=2 (Here x is >2 so x++ executed and now x is 4);
z=4 x=5 y=2(Here also x+ executed and x is 6 now)

So o/p should be x=6and y=2 but why it is mentioned in answers as

x=8 and y=2?


One more is

Class test{
public static void main(String arg[])
{
int x=0,y=0;
for(int z=0;z<5;z++)
{
if((++x>2)&&(++y>2))
{
x++;
}
}
System.out.println(x + " " +y);
}

}

I traced it as follows

z=0 x=1 y=0
z=1 x=2 y=0
z=2 x=3 y=1(the && condition is true so x++ evaluated and x is now 4)
z=3 x=5 y=2(here x++ excecuted and x is 6 now)
z=4 x=7 y=3

so o/p should be x=7 and y=3 right?
but it is mentioned as x=6 and y=3

where I go wrong?

[marc weber]

Try adding some println statements to show what the code is doing. For example...

class Test {
  public static void main(String[] args) {
    int x = 0;
    int y = 0;
    for(int z = 0; z < 5; z++) {
      [B]System.out.println("z is " + z);[/B]
      if((++x > 2)||(++y > 2)) {
        [B]System.out.println("True: x is " + x + ", and y is " + y);[/B]
        [B]System.out.println("Incrementing x again...");[/B]
        x++;
      }
      [B]else System.out.println("False: x is " + x + ", and y is " + y);[/B]
    }
    System.out.println(x + " " + y);
  }
}

[ July 19, 2007: Message edited by: marc weber ]

[Shrikanth Nekkanti]

Mr vats rao

U missed one value of z. thats why you have got wrong answer

Analyse like

z=0-->x=1,y=1
z=1-->x=2,y=2
z=2-->x=3,y=2
once ++x ie ++2 becomes 3 xbecomes 4
x=4
z=3-->x=5,y=2
here in loop X becomes 6
z=4-->x=7,y=2
here in loop x becomes 8

[Les Hayden]

I traced it as follows

z=0 x=1 y=0
z=1 x=2 y=0
z=2 x=3 y=1(the && condition is true so x++ evaluated and x is now 4)
z=3 x=5 y=2(here x++ excecuted and x is 6 now)
z=4 x=7 y=3

so o/p should be x=7 and y=3 right?
but it is mentioned as x=6 and y=3

At z=2, you say that "&& condition is true", but the y>2 condition actually returns false for another two iterations of the loop. The if's block does not execute until z=4.

[vatsalya rao]

Thank you all for pointing out ,where I went wrong.

[Israel Guerra]

Hail all!

It's a bit confusing this thing, but i got to the following conclusion:

z: 0 x: 1 y: 0 -> in the if condition, x is incremented
z: 1 x: 2 y: 0 -> again, the same thing
z: 2 x: 3 y: 1 -> x is incremented again, so the first part of the teste is true, making y also be incremented (just remembering here that y was not incremented before because && does not check the second statement if the first is false)
z: 3 x: 4 y: 2 -> same situation explained in the las step
z: 4 x: 6 y: 3 -> now we have the if scope executed so x is incremented 2 times.

Think its that!

Take care,