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