C# | Built-in Types

Conversion of boxed value types

Boxed value types can only be unboxed into their original Type, even if a conversion of the two Types is valid, e.g.:

object boxedInt = (int)1; // int boxed in an object

long unboxedInt1 = (long)boxedInt; // invalid cast

This can be avoided by first unboxing into the original Type, e.g.:

long unboxedInt2 = (long)(int)boxedInt; // valid

Immutable reference type - string

// assign string from a string literal
string s = "hello";

// assign string from an array of characters
char[] chars = new char[] { 'h', 'e', 'l', 'l', 'o' };
string s = new string(chars, 0, chars.Length);

// assign string from a char pointer, derived from a string
string s;
unsafe
{
    fixed (char* charPointer = "hello")
    {
        s = new string(charPointer);
    }
}

Value type - char

// single character s
char c = 's';

// character s: casted from integer value
char c = (char)115;

// unicode character: single character s
char c = '\u0073';

// unicode character: smiley face
char c = '\u263a';

Value type - short, int, long (signed 16 bit, 32 bit, 64 bit integers)

// assigning a signed short to its minimum value
short s = -32768;

// assigning a signed short to its maximum value
short s = 32767;

// assigning a signed int to its minimum value
int i = -2147483648;

// assigning a signed int to its maximum value
int i = 2147483647;

// assigning a signed long to its minimum value (note the long postfix)
long l = -9223372036854775808L;

// assigning a signed long to its maximum value (note the long postfix)
long l = 9223372036854775807L;

It is also possible to make these types nullable, meaning that additionally to the usual values, null can be assigned, too. If a variable of a nullable type is not initialized, it will be null instead of 0. Nullable types are marked by adding a question mark (?) after the type.

int a; //This is now 0.
int? b; //This is now null.

Value type - ushort, uint, ulong (unsigned 16 bit, 32 bit, 64 bit integers)

// assigning an unsigned short to its minimum value
ushort s = 0;

// assigning an unsigned short to its maximum value
ushort s = 65535;

// assigning an unsigned int to its minimum value
uint i = 0;

// assigning an unsigned int to its maximum value
uint i = 4294967295;

// assigning an unsigned long to its minimum value (note the unsigned long postfix)
ulong l = 0UL;

// assigning an unsigned long to its maximum value (note the unsigned long postfix)
ulong l = 18446744073709551615UL;

It is also possible to make these types nullable, meaning that additionally to the usual values, null can be assigned, too. If a variable of a nullable type is not initialized, it will be null instead of 0. Nullable types are marked by adding a question mark (?) after the type.

uint a; //This is now 0.
uint? b; //This is now null.

Value type - bool

// default value of boolean is false
bool b;
//default value of nullable boolean is null
bool? z;
b = true;
if(b) {
    Console.WriteLine("Boolean has true value");
}

The bool keyword is an alias of System.Boolean. It is used to declare variables to store the Boolean values, true and false.

Comparisons with boxed value types

If value types are assigned to variables of type object they are boxed - the value is stored in an instance of a System.Object. This can lead to unintended consequences when comparing values with ==, e.g.:

object left = (int)1;  // int in an object box
object right = (int)1; // int in an object box

var comparison1 = left == right;      // false

This can be avoided by using the overloaded Equals method, which will give the expected result.

var comparison2 = left.Equals(right); // true

Alternatively, the same could be done by unboxing the left and right variables so that the int values are compared:

var comparison3 = (int)left == (int)right; // true