Compiler Design Test Series Question

Question

What is the correct answer to this problem? In the key, the answer is given as A but I'm getting C. Please tell me why it is so. Thanks.

Comments

D)????

---

Please explain how you got D? Btw the answer given in key is A.

---

how r u getting C???

---

C looks correct to me.

---

yes, C is correct.

---

@ joshi_nitish

In option A) it is told

A.evenx=!(A1.evenx)

So, how do u determine x is even here?

x could be even as well as odd

rt?

---

yes Answer is C, ACE has given wrong answer.

Answer 1

https://gateoverflow.in/171923/ace-test-series

This Question is already asked and It's ans should be C

Comments

No explanation is provided at all there. Concluding something without any proper reasoning is not the right way to prepare.

---

In that link that Q is asked for just confirmation. and here explanation was not discussed.
Anyway here's is explanation :

evenx is a Boolean variable which keeps track if number of x are even or odd
If number of x's in A or A1 are even then A.evenx = true or A₁.evenx = true respectively
if x's are odd in A or A1 then A.evenx or A₁.evenx = false respectively

A.n and A₁.n counts number of x's in A and A₁ respectively.

In option A)
If A₁.evenx = true (i.e. there are even number of x's in A₁.)
then obviously A.evenx = odd

and vice versa.

(Because A.evenx will be A₁.evenx + 1 : how?
because A = xA₁y
hence to the string A₁, x and y are concatenated. and that's why number of x's in A will be 1 more than number of x's in A₁.)

In option B)
With the help of above explanation to find number of x's in A we need to calculate (A.n % 2).
(A.n % 2) ==0 then it will return "true" and that value will be assigned to A.evenx.

Hope you'll get it :)

And hence both A and B are correct, Hence answer is C

Answer 2

Yes Ans should be option C.