Why I cannot initialize double as null

Question

2.46/5 (4 votes)

See more:

Hi,

I am initializing double type as null in my program

C#

double utilization1=null;
            double utilization2=null;
            double utilization3=null;
            double utilization4 = null;

And I am using a condition as below in my program

C#

if ((utilization1 != null) && (utilization2!=null)&&(utilization3 != null) && (utilization4!=null))
           {

            //do something
           }

I am getting error like below

C#

Cannot convert null to 'double' because it is a non-nullable value type

Can anyone help me in solving this problem

Posted 18-Feb-14 4:31am

Member 10408451

Add a Solution

Comments

Richard MacCutchan 18-Feb-14 10:40am

Initialise the values to zero.

Sergey Alexandrovich Kryukov 18-Feb-14 13:04pm

Not a good idea. Something like NaN is usually more appropriate.
—SA

Krunal Rohit 18-Feb-14 10:44am

Ignore the following advice, it's complete garbage:

Try this,
double x;
x = double.Nan;
or x = null;

6 solutions

Solution 6

In addition to using nullable double?, you can also use NaN (Not a Number):
http://msdn.microsoft.com/en-us/library/system.double.nan(v=vs.110).aspx[^],
http://msdn.microsoft.com/en-us/library/system.double.isnan(v=vs.110).aspx[^],
see also http://msdn.microsoft.com/en-us/library/system.double%28v=vs.110%29.aspx[^].

In most cases, this is the most adequate approach, lightweight compared to using the nullable type.

—SA

Posted 18-Feb-14 7:07am

Sergey Alexandrovich Kryukov

Updated 18-Feb-14 7:08am

v2

Solution 4

Use Nullable Types[^].

C#

int? i = 10;
double? d1 = 3.14;
bool? flag = null;
char? letter = 'a';

-KR

Posted 18-Feb-14 4:46am

Krunal Rohit

Comments

Sergey Alexandrovich Kryukov 18-Feb-14 13:15pm

Voted 4. You are missing the possibility specific to floating-point types: using NaN, which is more light weight and more adequate in most cases. Please see Solution 6.
(Two votes of 1 are just amazing though. Who is that "clever"? :-)
—SA

Solution 5

Because it's a Value Type[^]

If you want it to be null you have to define it this way:

C#

Nullable<double> utilization1 = null;

if ((utilization1.HasValue)
{
  //Do Something with utilization1.Value
}

</double>

Hope it helps

Posted 18-Feb-14 4:47am

_Zorro_

Comments

Sergey Alexandrovich Kryukov 18-Feb-14 13:10pm

Voted 4. You are missing the possibility specific to floating-point types: using NaN, which is more light weight and more adequate in most cases. Please see Solution 6.
—SA

_Zorro_ 19-Feb-14 8:04am

Thanks for pointing this out. Never used that, I'll keep that in mind.

Sergey Alexandrovich Kryukov 19-Feb-14 10:40am

Sure.
—SA

Solution 1

Because System.Double is a value-type, not a reference-type; so it cannot be null. Better initialize it to zero.

Posted 18-Feb-14 4:42am

phil.o

Comments

Sergey Alexandrovich Kryukov 18-Feb-14 13:14pm

First part it true, the rest of it is wrong. Please see other answer. Zero is probably the worst idea. How can you tell the difference between uninitialized 0 and 0 which is normal data? It's much better to use NaN.
—SA

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Pete O'Hanlon · Accepted Answer · 2014-02-18T04:43:00

Solution 2

You'll find that the value types are not nullable types by default (reference types are). To make it a nullable type, you change the way you declare double to be double?. Notice the question mark after the type declaration - this is the shorthand way of defining a type as nullable. What this is actually doing is the equivalent of using the System.Nullable<double> generic to create a nullable type of double.

Posted 18-Feb-14 4:43am

Pete O'Hanlon

Comments

Sergey Alexandrovich Kryukov 18-Feb-14 13:10pm

Voted 4. You are missing the possibility specific to floating-point types: using NaN, which is more light weight and more adequate in most cases. Please see Solution 6.
—SA

Vishveshs · Accepted Answer · 2014-02-18T04:45:00

Solution 3

'double' is value type and value type cannot contain the null value.
If you want initialize variable with null value then you should use 'double?' instead of double.

double? utilization1=null;

if (utilization1.hasvalue)
{
//do something
}

Posted 18-Feb-14 4:45am

Vishveshs

Comments

agent_kruger 18-Feb-14 11:02am

[Not an answer] sir, i just want to ask from were have you learnt this? did you search on internet or learnt it from somewhere.

Sergey Alexandrovich Kryukov 18-Feb-14 13:12pm

If you are so ignorant and helpless, don't think that others are like that. These are way too elementary facts.
And let me ask you, why do you think this is not an answer? And is it why you voted 1 everywhere? Why?
—SA

agent_kruger 18-Feb-14 14:03pm

no sir, i said to my comment that it is off topic and not an answer.

Pete O'Hanlon 18-Feb-14 16:29pm

Why do you think it's off topic and not an answer? This answer has explained that value types cannot contain null, and it has shown how to write the code so that a value type can be null. You do know that a double is a value type don't you? So, I'm sorry, but you are wrong and you need to learn more about .NET before you start downvoting people.

Sergey Alexandrovich Kryukov 18-Feb-14 17:58pm

Agree. Why would OP say "no sir"? I say that OP indicated it's "[Not an answer]" and this is not true. The answer does provide the mechanism to indicate "no initialized" value...
—SA

agent_kruger 18-Feb-14 22:50pm

sir, you are not getting it, i said "my comment" is off topic and is not an answer

Sergey Alexandrovich Kryukov 18-Feb-14 23:28pm

Oh gosh. Sorry. Now I got it...
—SA

agent_kruger 18-Feb-14 22:51pm

sir, you are not getting it, i said "my comment" is off topic and is not an answer

agent_kruger 18-Feb-14 14:19pm

and i am not the one to vote every one 1 i justed voted 1 to 2 people.

Sergey Alexandrovich Kryukov 18-Feb-14 18:01pm

Whatever. If I can see that your comment is inadequate and not true, I could have some reasons to assume your votes are not adequate.
I looks like you are missing something from the answers you got.
—SA

Sergey Alexandrovich Kryukov 18-Feb-14 13:11pm

Voted 4. You are missing the possibility specific to floating-point types: using NaN, which is more light weight and more adequate in most cases. Please see Solution 6.
—SA