ISRO2015-69

Question

If n has  3, then the statement a[++n]=n++;

• A. assigns 3 to a[5]
• B. assigns 4 to a[5]
• C. assigns 4 to a[4]
• D. what is assigned is compiler dependent

Answer 1

It is compiler dependent

Reference :Undefined behaviour

Comments

@manoj sir, codepad give 6 

                 tutorial point give 5

                  ideaone give 5.         why?

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That is what is undefined behavior of C.

i = i++

which modify the same value twice which needn't be allowed.

Similarly here

a[i] = i++

which modify i and use it along the way.

Its all depends on compiler what value is will be assigned .

I think it should be clear . I dont know much about undefined stuffs.

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Final value of i is 6

Answer 2

It is an undefined behaviour since between two sequence points which is here ; at the end of this statement and the other ; which would be present above this statement in the actual code we cannot modify the value of a variable more than once therefore here u r trying to modify the value of n two times so it depends on compiler wither it will evaluate ++n inside array subscript or assign ++n to array index .

Answer 3

Ans is D.It depends on the compiler.Here n is updated twice before the next sequence point is reached.ref:https://en.wikipedia.org/wiki/Sequence_point

Comments

So whenever there are 2 or more modifications on the same variable, it is always compiler dependent?

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No. It is about how and in which order prefix and postfix operator perform its function

Answer 4

Answer : option C- assigns 4 to a[4]