Null-coalescing operator

Question

I have the following code:

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.

However, the result I get is 2, in which case b is taken as 1 instead of 2.

Does anyone know what is the reason behind this behaviour?

John Woo · Accepted Answer · 2012-09-28 02:08:53Z

group the value condition if you want to get the value of 4

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

your current syntax is evaluated as

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

and the reason why you get the value of 2 (as for a)

Guffa · Accepted Answer · 2012-09-28 02:03:44Z

4

The expression works as:

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

As a has a value, you get that.

answered Sep 28, 2012 at 2:03

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Comments

gdoron · Accepted Answer · 2012-09-28 02:03:31Z

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

Equals to:

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

In your case a is not null and has the value of 2 so this is the result.