What Does the Question Mark Mean When Used with Value Types in C#?

The role of question marks in C# value types

While the question mark is typically used in conditional statements (e.g., x ? "yes" : "no" ), it also has a different purpose in the context of value types.

Nullable value type

In C#, a question mark after a value type (for example, int? myVariable) indicates that the value type is nullable. This means that it can represent not only the standard value range of the underlying data type, but also the special null value.

For example, Nullable can take on any integer value between -2,147,483,648 and 2,147,483,647, and can also be assigned the null value. Nullable types are particularly useful when dealing with databases or other situations where data may be missing or unassigned.

Advantages of nullable types

Nullable types have the following advantages:

• Accurate representation of unknown data: They allow missing or unassigned values ​​to be correctly represented in data structures.
• Safe assignment of null values: Use nullable types to ensure that null values ​​are handled explicitly, thus preventing errors and crashes.
• Consistent handling of null values: Nullable types provide a consistent way to handle null values, simplifying code development and maintenance.

Example usage

The following code snippet demonstrates the use of nullable integer values:

class NullableExample
{
  static void Main()
  {
    int? num = null;

    if (num.HasValue)
      System.Console.WriteLine("num = " + num.Value);
    else
      System.Console.WriteLine("num = Null");

    int y = num.GetValueOrDefault();

    try
    {
      y = num.Value;
    }
    catch (System.InvalidOperationException e)
    {
      System.Console.WriteLine(e.Message);
    }
  }
}

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