Unexpected output ??

[Rao Rekha]

Could anyone kindly let me know why does the following code prints 3 ?
class TestClass
{
public static void main(String args[])
{
boolean b = false;
int i = 1;
do
{
i++ ;
} while (b = !b);
System.out.println( i );
}
}
Thanks in advance.

[Gautam Jha]

Because of "(b = !b)" in the "while" statement.
Note its an assignment and not an check. After
the assignment, the value of b is used to determine whether to quit the loop or not? Make sense??

[Chitra Jay]

class TestClass 
{
public static void main(String args[]) 
{
boolean b = false;
int i = 1;
do 
{
i++ ;
} while (b = !b);
System.out.println( i );
}
}

do-while loop executes its body atleast once irrespective of whether the condition returns true/false
i gets incremented to 2
goes thru the condition in while
b= !b
in this statement,! has higher precedence than =.
!b evaluates to !false ==> true
now b gets assigned the value true.
(b = (!false)) -> true
since the condition returns true,it enters the loop again,and increments i to 3.
Now,the condition is evaluated once again,
but returns false (because b = (!true) )therefore comes out of the loop and prints 3.
Chitra

[Rao Rekha]

That makes complete sense. Thanks Jha and Chitra.