空结合运算符

Question

I have the following code: 我有以下代码：

decimal? a = 2m;
decimal? b = 2m;
decimal c = a ?? 1m * b ?? 1m;

Since both a and b have been filled in, I'm expecting c to give me the result of 4 . 由于a和b都已填写，我期待c给我4的结果。

However, the result I get is 2 , in which case b is taken as 1 instead of 2 . 但是，我得到的结果是2 ，在这种情况下， b被视为1而不是2 。

Does anyone know what is the reason behind this behaviour? 有谁知道这种行为背后的原因是什么？

Answer 1

group the value condition if you want to get the value of 4 如果要获取值4则将值条件分组

decimal c = (a ?? 1m) * (b ?? 1m);

your current syntax is evaluated as 您当前的语法被评估为

decimal c = a ?? (1m * b ?? 1m);

and the reason why you get the value of 2 ( as for a ) 以及你得到2的值的原因（ 至于a ）

Answer 2

The expression works as: 表达式如下：

decimal c = a ?? (1m * b) ?? 1m;

As a has a value, you get that. 作为a有价值，你得到了。

Answer 3

decimal c = a ?? 1m * b ?? 1m;

Equals to: 等于：

if (a != null)
    c = a
else
    ...

In your case a is not null and has the value of 2 so this is the result. 在您的情况下， a不为null并且值为2因此这是结果。