Operator mock exam question

[Connie Ky Leung]

   

class Compound{
public static void main(String args[])
{
int k=12;
k/=--k;
System.out.println(k);
k*=k++;
System.out.println(k);
k*=++k;
System.out.println(k);
}
}

This mock exam question is from javachampion.com.
The output is 1 1 2
Can someone explain how the result is produced?
I don't know how to trace it on paper.

Thanks,

Connie

[Christophe Verré]

There are some explanations here.

[Abimaran Kugathasan]

Have a look on this also.

k *= k++;

interpreted as

 k = k * (k++);

[Unmesh Chowdhury]

int k = 12;

Line 7:
k/=--k;

or, k = k / --k
or, k = 12 / 11
or, k = 1
Line 8:
Print 1

Line 9:
k*=k++;

or, k = k * k++
or, k = 1 / 1
or, k = 1
Line 10:
Print 1

Line 11:
k*=++k;

or, k = k * ++k
or, k = 1 * 2
or, k = 2
Line 12:
Print 2

[Mahmoud Hossam]

will the exam contain complex arithmetic questions?

like this one for instance

[Abimaran Kugathasan]

Unmesh Chowdhury wrote:

or, k = k / --k
or, k = 12 / 11 // Check here!
or, k = 1

It should be 12

[Unmesh Chowdhury]

@Abimaran Kugathasan
Explain how?

There is no scope of should be.

[Unmesh Chowdhury]

Let’s see how the k = k / --k statement is evaluated as k = 12 / 11 statement.

Initially, k = 12.

k = k / --k, is an assignment statement so the right hand expression will be evaluated first.

Now, k / --k expression will be evaluated from left to right.

k is evaluated as 12 and the value is loaded into the processor register or into the processor cache memory (according to the processor architecture) from the physical memory (RAM).

--k is a pre-decrement and single expression. When it is evaluated, there are two things will be happened – the value of its will be decreased by 1 and a value will be returned. Since it is a pre-decrement expression so the new value will be returned, that is, 11 will be returned. So, --k is evaluated as 11 and the value is loaded into the processor register as usual.

So, the k / --k expression is evaluated as 12 / 11.

(The rest of the story, that is, the execution of the simple integer arithmetic is done by the processor and returns the value accordingly which is 1 and the value is assigned into the k variable.)

In the case of post-increment or post-decrement, the evaluation is done in the same way but return the previous value.

[Abimaran Kugathasan]

Abimaran Kugathasan wrote:

Unmesh Chowdhury wrote:

or, k = k / --k
or, k = 12 / 11 // Check here!
or, k = 1

It should be 12

Sorry, it's my mistake. It should be 11. because of the implicit casting, 1 will assign to k, even though the the result if float value.