+ =和= +之间的差异 [英] The difference between += and =+

问题描述

我错了+ = = = +一次多次，我想我一直都忘了因为我不知道这两者之间的区别，只有那一个给了我期望它的价值，而另一个没有。

I've misplaced += with =+ one to 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（尽管请注意表达式 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 是 a =（+ b），即分配一元 + b 到 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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