c# - 十进制可空值和十进制值的总和

Question

为什么在此代码执行后变量 'a' 包含 null 而不是 10？

decimal? a = null;
a += 10;

Answer 1

您不能将值添加到 null。 null 将为 null 添加任何值。另一方面，如果您已将非空值分配给 a，则 10 将被添加到 a。

取自MSDN

The predefined unary and binary operators and any user-defined operators that exist for value types may also be used by nullable types. These operators produce a null value if the operands are null; otherwise, the operator uses the contained value to calculate the result. For example:

int? a = 10;
int? b = null;

a++;         // Increment by 1, now a is 11.
a = a * 10;  // Multiply by 10, now a is 110.
a = a + b;   // Add b, now a is null.