Why am I getting "CS0472: The result of the expression is always true since a value of type int is never equal to null of type int?"

string[] arrTopics = {"Health", "Science", "Politics"};

I have an if statement like:

 if (arrTopics.Count() != null)

When I hover my mouse over the above statement, it says:

Warning CS0472: The result of the expression is always true since a value of ty开发者_StackOverflowpe int is never equal to null of type int?

I am not able to figure out why it is saying so. Can anybody help me?

int can never be equal to null. int? is the nullable version, which can be equal to null.

You should check if(arrTopics.Count() != 0) instead.

What are you trying to ask here?

   Array.Count() returns an int which will never be null.

If you want to know if the Array has been initialised then:

   if(arrTopics !=null) ...

if you want to know if it's been initialised but has no members then:

  if(arrTopics.Count() > 0) ...

null represents the absence of any value, not the number 0. And as the message says an int can never be null since it's neither a reference type nor a nullable value type and thus always has some value.

It means what it says.

The "Count" method returns a value type. It's an integer. It will always have a value where it's default value is zero.

Your check really should be:

if (arrTopics.Count() != 0)

Like the error says, int can never be null. I'd change the code to

if (arrTopics != null && arrTopics.Any())

Or even more efficient if you know arrTopics is an array and never null is

arrTopics.Length != 0

Null is a special pointer value, and not an integer. There are nullable types, that are either null or one of the possible values for the base type, but int itself is not nullable.

Because Count method always returns integer if no elements in array it will return 0 other wise it will return number of elements. So what you need to do is just instead != null make it != 0 or > 0

To figure it out, look into geclaration of Count() extension method.

Puzzle of two pieces:

1. You are trying to compare non-nullable type (value of type int) with null, so non-nullable types is never being referenced to, because all non-nullable types are value types in C#, which can not be referenced.

2. Inequality defined through equality oerator in object class, which is defined in base. so your code mentioned above can be perfectly valid. Unfortunately, to distinguish situation when this appearance of equality operator in not desired (not overridden) in base classes there are some compiler warinings about it, because you will really get a always-false condition for incompatible types (or get an always-true condition in inequality operator)

And value types (non-nullable) and nullable types (referenced types) are incompatible types in C#. For more info look into ECMA papers for standart of definition for type system being used in a C# language.

Your if statement doesn't look right. I assume. You either meant to

if(arrTopics?.Count() != null)

OR

if (arrTopics.Any())

OR

if (arrTopics != null)

Explanation: sequence.Count() returns int which is never null. Adding the question mark ? returns Nullable<int> instead of int. Also Count() expects the sequence to be instantiated. using Count() method on a null sequence results in ArgumentNullException; so you always need to check against null reference, before going for Count(), Any() extension methods, or use the question mark.