Can anyone tell me why is the output of this code is 13579 😵

Question

I was challenging someone in Java .. and I got this question

//what is the output of this code?

boolean b=true ;
for (int i = 0 ; i <10 ; i++)
if (b = !b) System.out.print (i) ;

the Answer was 13579 .. I see that it took only the odd numbers ..
But why! 🤔
I really tried to understand it on my own.. but I don't get it.
anyway.. thanks for helping ✌️😁

Answer 1

false 0 //b= !true ... ie false
true 1 //b=!false ... ie true
false 2 //false
true 3 //true
.
.
it goes in alternate order
//loop goes from 0 to 9 .... 1 3 5 7 9

Answer 2

Saeed Boss
When you write b=!true...
In every iteration b=false
Hence the condition if(b=!true), becomes false
Therefore, no output is displayed...
I hope it helps!

Answer 3

Thats tricky because you thought b=!b is checking for similarity.

Answer 4

boolean b=true ;
for (int i = 0 ; i <10 ; i++)
if (b=!b) System.out.print (i);

In the beginning "b=true"
for i=0--->b=false--->no output
for i=1--->b=true--->output =1
for i=2--->b=false--->no output
for i=3--->b=true--->output =3
.
.
.
In every iteration, 'b' is assigned with a value which is the opposite to itself...

When 'i' is even... Output is not displayed, because b=false

When 'i' is odd... Output is displayed, because b=true

Answer 5

it's just because of (b = !b), coz at every iteration you're assigning the opposite value of b.

Answer 6

This problem is somewhat misleading, especially to novice programmers. Starting from the answer itself, 13579, which has to be 1 3 5 7 9.

In order to understand this problem and see what's going on under the hood, try to change the way the program outputs the answer on the screen by doing the following:

for (int i = 1; i < 10; i += 2)
{
//System.out.printf("%d", i);
System.out.println(i);
}
Now, your output should look like this:
1
3
5
7
9

It's just the difference between printf() and println(). The first prints i on the same line for each iteration and the result is 13579, while the latter prints the result for each iteration on a new line. So, the result 13579 has nothing to do with the number of iterations or the sum of i after executing the loop, because it's simply the numbers 1, 3, 5, 7, and 9 joined altogether on the same line!

Try also the following:

for (int i = 1; i < 10; i += 2)
{
System.out.printf("%d ", i);
}
The output now is:
1 3 5 7 9

I hope that helps..

Answer 7

How about if i changed this if(b = !b) to this if( b = !true) aren't they same?

boolean b = true;