运算符优先级练习

执行以下语句会打印出？

int arr[] = {6, 7, 8, 9 ,10};
int* ptr = arr;
*(ptr++) += 123;
cout<<*ptr<<endl;

先看看运算符的优先级，一般容易考察的是红色的这几个：

Precedence	Operator	Description	Associativity
1	::	Scope resolution	Left-to-right
2	++ --	Suffix/postfix increment and decrement (a++)
()	Function call
[]	Array subscripting
.	Element selection by reference
−>	Element selection through pointer
3	++ --	Prefix increment and decrement (++a)	Right-to-left
+ −	Unary plus and minus
! ~	Logical NOT and bitwise NOT
(type)	Type cast
*	Indirection (dereference)
&	Address-of
sizeof	Size-of
new , new[]	Dynamic memory allocation
delete , delete[]	Dynamic memory deallocation
4	.* ->*	Pointer to member	Left-to-right
5	* / %	Multiplication, division, and remainder
6	+ −	Addition and subtraction
7	<< >>	Bitwise left shift and right shift
8	< <=	For relational operators < and ≤ respectively
> >=	For relational operators > and ≥ respectively
9	== !=	For relational = and ≠ respectively
10	&	Bitwise AND
11	^	Bitwise XOR (exclusive or)
12	|	Bitwise OR (inclusive or)
13	&&	Logical AND
14	||	Logical OR
15	?:	Ternary conditional	Right-to-left
=	Direct assignment (provided by default for C++ classes)
+= −=	Assignment by sum and difference
*= /= %=	Assignment by product, quotient, and remainder
<<= >>=	Assignment by bitwise left shift and right shift
&= ^= |=	Assignment by bitwise AND, XOR, and OR
16	throw	Throw operator (for exceptions)
17	,	Comma	Left-to-right

所以这句应该解释为：

*(ptr++) += 123;

*ptr = *ptr + 123; ptr++;  括号中的内容先执行，得到前一语句；ptr再进行自增；

ptr的自增应该是在第一条语句执行之后发生的，这样才合理，否则*(++ptr) += 123的执行结果就不好解释了，写编译器的人肯定也需要语句执行的结果合理才能自圆其说的！

答案： 7