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Pedro Ávila
Asked: 2020-04-01 14:18:08 +0800 CST 2020-04-01 14:18:08 +0800 CST

operator ? when writing data types

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I am curious and I want to get rid of the doubt, in which cases a variable is declared in the following way:

public short? Secuendia {get; set;}

What does the question mark mean and in which cases the data type is accompanied by a character?

c#

2 Answers

  1. The character ?is used in types to indicate the value is nullable , that is, it can be a valid number or it can be null.

    They are known as Nullable Types , and can represent the normal range of numbers of the specified type plus the null value.

    In practice they are instances of the structure System.Nullable<T>, therefore it has some methods.

    Example:

    int? num = null;

// tiene valor en num
if (num.HasValue)
{
    System.Console.WriteLine("num = " + num.Value);
}
else
{
    System.Console.WriteLine("num = Null");
}

    In Booleans, it is used to represent tristate or three-state values.

    bool? tristate; // puede ser true, false o null
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  2. Best Answer

    The type declaration ?is used when you use a data type that cannot be, nullfor example, a Structure and you force it to be null, this is achieved by marking with the operator?

    This is called Nullable

    You can check more here: Operator ??

    Difference against a normal statement

    int a;
int? b;

a = 5;//ok
b = 5;//ok

a = null; //Error: Cannot convert null to 'int' because it is a non-nullable value type
b = null;//ok
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