我可以直接在“ if”表达式中声明一个对象吗？

Question

I am trying to use an object just for an expression but not sure if that is possible:

if ((new (Random)).Next(0,1))
{

}

This does not work, I would like to know whether it is even possible?

Answer 1

This will work... Note that what you wrote had multiple errors (logical and grammar)

if (new Random().Next(0,2) == 0)

And you aren't declaring an object, you are creating an object.

The syntax to create an object is new TypeName() or new TypeName {} . If the constructor has parameters, you have to use the syntax new TypeName(par1, par2) .

Doing a new Random().Next(0, 1) is totally useless... because it will generate a random number between 0 and 1 excluded, so 0 and 0, so 0 :-)

Other "logical" error: a Random object should be reused, not created and used once and then discarded. This because a Random object "represents" a sequence of random numbers (based on the seed). If you create multiple Random objects in a short time, they'll often use the same seed, and generate the same sequence. new Random().Next() == new Random().Next() 99 times out of 100.

You can even do more awful things (note the bold)...

Random rnd;

if ((rnd = new Random()).Next(0, 2) == 0)

This because the assignment operator = "returns" the value assigned, so you are assigning new Random() to rnd , and then you are taking the assigned value and using it for the .Next . Note the additional brackets around the assignment.

If your question is really Can I declare an object directly in the “if” expression? , then the answer is no! You can't declare a new variable inside the if conditional expression... You can't do:

if ((Random rnd = new Random()).Next(0, 2) == 0)

The only keyword in C# that lets do it are the for cycle :

for (Random rnd = new Random()...

and the using (but this one is more limited, it can only work in IDisposable )

Answer 2

You need to initialize it using () . It still doesn't return any boolean result which is must for an if condition.

Do it like this:

if (new Random().Next(0,2) == 1)

Answer 3

This is not possible because

1. if condition only check for boolean condition .ie true or false
2. Your statement neither return true or false
3. You statement in if condition returns void (or the variable defined)

Answer 4

您需要将其更改为if（new Random（）。next（0,2）== 0）并且应该没有任何问题...