+= 和 =+ 的区别 [英] The difference between += and =+

问题描述

我多次将 += 与 =+ 放在一起，我想我一直忘记，因为我不知道这两者之间的区别，只是一个给了我我期望的价值，而另一个没有.

I've misplaced += with =+ one too many times, and I think I keep forgetting because I don't know the difference between these two, only that one gives me the value I expect it to, and the other does not.

这是为什么?

推荐答案

a += b 是 a = a + b 的简写(但请注意表达式 a 只会被评估一次.)

a += b is short-hand for a = a + b (though note that the expression a will only be evaluated once.)

a =+ b 就是a = (+b)，即赋值b的一元+a.

a =+ b is a = (+b), i.e. assigning the unary + of b to a.

示例:

int a = 15;
int b = -5;

a += b; // a is now 10
a =+ b; // a is now -5

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