Basic increment in C

Question

I have a very basic doubt, I tried the following code in C.

i=(++i)+(++i)+(++i);

I expected the answer to be 6 but the answer came out to be 7. How is it this possible ?increment in C

`i=0` would make sense, i.e. what OP is expecting - 1+2+3 = 6. — Bernhard Barker, Jun 21 '13 at 10:51
It does if you're expecting the answer to be 6! I would presume `i=0` since that would naively produce `i = 1 + 2 + 3` — Jack Aidley, Jun 21 '13 at 10:51
Irrespective of the answer, you should avoid such expressions. Its a bad programming practice. Code should be readable and not obfuscated. Most of such questions come up during interviews (I consider them bad interview questions!). — Atmaram Shetye, Jun 21 '13 at 11:02
@zaphod What if the interviewer wants a response "Yuck! Don't ever do that even in Java or C# where it's defined behaviour!"? — Daniel Fischer, Jun 21 '13 at 11:17
Yup, thats the right way to answer that question. "Yuck, I would never code in that manner!" ;) — Atmaram Shetye, Jun 21 '13 at 12:43

Sebastian Mach · Answer 1 · 2013-06-21T10:58:15.780

4

Assigning multiple times to a single memory location between two sequence points yields undefined behaviour, no certain value or behaviour is to be expected.

Rule of thumb: Do not assign multiple times to a single value within a single expression:

++i; ++i; i+= i; // okay
++i + ++i;       // not okay

edited Jun 21 '13 at 10:58

answered Jun 21 '13 at 10:53

Sebastian Mach

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Assigning multiple times to a single memory location *in a single sequence point*. `i = i + 1; i = i + 1;` is fine ;). – Zeta Jun 21 '13 at 10:54
@Zeta, that makes much more sense. – Prof. Falken Jun 21 '13 at 10:54

Basic increment in C

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