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I am new to C. Sorry for such a basic question.

int ArrayIndex = 0;
int intArray[ArrayIndex++] = somevalue;

I have read a book that says when exactly postfix increment/decrement is performed is not a simple question to answer. The book also says vaguely about a concept called sequence points to answer the question. It says updating the value[incrementing/decrementing] will take place between the previous and next sequence point. The example for such a sequence point is end of an expression statement.

My question is, will the above code snippet always assign some value to array index zero and increment ArrayIndex, in all compilers/platforms? Is there a chance that ArrayIndex is incremented first and then somevalue is assigned to intArry[1];?

Can anybody shed some light?

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2 Answers 2

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My question is, will the above code snippet always assign some value to array index zero and increment ArrayIndex, in all compilers/platforms?

Answer: Yes

Is there a chance that ArrayIndex is incremented first and then somevalue is assigned to intArry[1];?

Answer: If you use 

int intArray[++ArrayIndex] = somevalue;

this will increment ArrayIndex and then assign value to array index 1

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++ArrayIndex increments ArrayIndex and evaluates to the new value of ArrayIndex.

ArrayIndex++ evaluates to the old value of ArrayIndex, and increments ArrayIndex.

This should answer your question. (Hint: the answer is yes).

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5 Comments

Naming conventions are quite irrelevant here to say the least.
@AlexeyFrunze You're right. As long as he's consistent this shouldn't bother.
It's not that. First, naming conventions weren't asked about. Second, they are subjective or specific to the team/project. Third, the question does not have low readability (like the poorly formatted long code you've seen in some other questions) due to the naming convention chosen. So, there's not a single objective reason to point at it at all.
@AlexeyFrunze Sometimes it doesn't hurt if you add additional notes/improvements even if they were not asked. But, as I said before, I agree with you in this case.. I shouldn't have mentioned it and that's why I edited my answer and removed it.
Sometimes yes, I agree, but not this time.

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