On Friday, 23 August 2024 at 08:58:16 UTC, Me'vâ wrote:
```
import std.stdio:writeln;
void main() {
int i = 5;
writeln("Result: ", i + ++i);
}
```
When I run this, it surprisingly outputs 11. I tried something
similar in C before and it gave me 12. I’m curious, why is
there a difference? How is i + ++i evaluated in D that it ends
up giving 11 instead of 12?
D: `5 + 6`
C++: undefined, could be `6 + 6` if the increment is done first.
g++ gives me a warning with `-Wall`:
```
inc.cxx: In function ‘int main()’:
inc.cxx:30:26: warning: operation on ‘i’ may be undefined
[-Wsequence-point]
30 | std::cout << i + ++i << "\n";
| ^~~
```
Is there something about operator precedence or evaluation
order in D that I'm missing? I'd really appreciate it if
someone could break it down for me or point me towards some
resources to get a better understanding of what's going on.
See https://dlang.org/spec/expression.html#order-of-evaluation
Binary expressions except for AssignExpression, OrOrExpression,
and AndAndExpression are evaluated in lexical order
(left-to-right).
So in D, the value of `i` on the left is always read before the
increment on the right.
