I have a curiosity 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 ?
The declaration type ? is used when you use a data type that can not be null for example a Structure and you force it to be null , this is achieved by dialing with the operator ?
This is called Nullable
You can check more here: Operator ??
Difference against a normal declaration
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
The ? character is used in types of to indicate the value is nulleable , so it can be a valid number or it can be null.
Known as Nullable Types , and may represent the normal range of numbers of the specific 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 Boolean it is used to represent tristate or three-state values.
bool? tristate; // puede ser true, false o null