Value types (C# Reference)
There are two kinds of value types:
Main features of value types
A variable of a value type contains a value of the type. For example, a variable of the
int type might contain the value
42. This differs from a variable of a reference type, which contains a reference to an instance of the type, also known as an object. When you assign a new value to a variable of a value type, that value is copied. When you assign a new value to a variable of a reference type, the reference is copied, not the object itself.
All value types are derived implicitly from the System.ValueType.
Unlike with reference types, you cannot derive a new type from a value type. However, like reference types, structs can implement interfaces.
Value type variables cannot be
null by default. However, variables of the corresponding nullable types can be
Each value type has an implicit parameterless constructor that initializes the default value of that type. For information about default values of value types, see Default values table.
The simple types are a set of predefined struct types provided by C# and comprise the following types:
The simple types are identified through keywords, but these keywords are simply aliases for predefined struct types in the System namespace. For example, int is an alias of System.Int32. For a complete list of aliases, see Built-in types table.
The simple types differ from other struct types in that they permit certain additional operations:
Simple types can be initialized by using literals. For example,
'A'is a literal of the type
2001is a literal of the type
You can declare constants of the simple types with the const keyword. It's not possible to have constants of other struct types.
Constant expressions, whose operands are all simple type constants, are evaluated at compile time.
Initializing value types
Local variables in C# must be initialized before they are used. For example, you might declare a local variable without initialization as in the following example:
You cannot use it before you initialize it. You can initialize it using the following statement:
myInt = new int(); // Invoke parameterless constructor for int type.
This statement is equivalent to the following statement:
myInt = 0; // Assign an initial value, 0 in this example.
You can, of course, have the declaration and the initialization in the same statement as in the following examples:
int myInt = new int();
int myInt = 0;
Using the new operator calls the parameterless constructor of the specific type and assigns the default value to the variable. In the preceding example, the parameterless constructor assigned the value
myInt. For more information about values assigned by calling parameterless constructors, see Default values table.
With user-defined types, use new to invoke the parameterless constructor. For example, the following statement invokes the parameterless constructor of the
var p = new Point(); // Invoke parameterless constructor for the struct.
After this call, the struct is considered to be definitely assigned; that is, all its members are initialized to their default values.
For more information about the
new operator, see new.
For information about formatting the output of numeric types, see Formatting numeric results table.