CODEWITHSUNDEEP
c#typesint
prathapa reddy
prathapa reddy

Reputation: 331

what is "int?" in C# types

I've seen this code sample question in a exam and it works perfectly.

namespace Trials_1
{
    class Program
    {
        static void Main(string[] args)
        {
            int? a = 9;
            Console.Write("{0}", a);
        }
    }
}

But the below code throws an error CS0266.

namespace Trials_1
{
    class Program
    {
        static void Main(string[] args)
        {
            int? a = 9;
            int b = a;
            Console.Write("{0},{1}", a, b);
        }
    }
}

Can somebody explain me in detail?

Upvotes: 7

Views: 16837

Answers (6)

lucaspompeun
lucaspompeun

Reputation: 308

Means that the variable declared with (int?) is nullable

int i1=1; //ok
int i2=null; //not ok

int? i3=1; //ok
int? i4=null; //ok

Upvotes: 2

Stef Geysels
Stef Geysels

Reputation: 1047

If you want to convert an int? to int, you have to cast it:

int? a = 9;
int b = (int)a;

Or:

int b = a.Value;

B.t.w: this woont give any problem:

int a = 9;
int? b = a;

Upvotes: 2

sujith karivelil
sujith karivelil

Reputation: 29016

The variable b is of type int and you are trying to assign int? to an int. which will be wrong assignment(if a is null, then you cannot assign it to non-nullable object b, so compiler will not permit this): alternatively you can use:

int? a = 9;
int b = a == null ? 0 : 1;
Console.Write("{0},{1}", a, b);

Upvotes: 0

Anonymous Duck
Anonymous Duck

Reputation: 2978

This is a C# nullable types

Nullable types represent value-type variables that can be assigned the value of null. You cannot create a nullable type based on a reference type. (Reference types already support the null value.)

This line int b = a; throws an error because you cannot directly assign an int type into a nullable int type. In other words, int datatype cannot accept null value.

Upvotes: 3

TimS
TimS

Reputation: 2113

int? is shorthand for Nullable<int> and indicates that a value of null can be assigned to the variable.

In the example given, the type of variable b is an int, which cannot accept a value of Nullable<int>.

Refer to This MSDN article for more information.

Upvotes: 2

Blue
Blue

Reputation: 22911

Some info on error CS0266:

Cannot implicitly convert type 'type1' to 'type2'. An explicit conversion exists (are you missing a cast?) This error occurs when your code tries to convert between two types that cannot be implicitly converted, but where an explicit conversion is available.

A nullable int (int?) cannot be converted simply converted to an int. An int by default cannot be null, so trying to convert something that can be null, to something that can't be null, gives you this error. Because you're trying to make this assumption, the compiler is telling you, you can't.

See this post on how to convert from a nullable int to an int.

Upvotes: 0

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