C# 2008 Programmer's Reference

double	System.Double	64	Signed 64-bit floating point number; approximately from ±5.0×10-324 to ±1.7×10308
float	System.Single	32	Signed 32-bit floating point number; approximately from ±1.5×10-45 to ±3.4×1038
int	System.Int32	32	Signed 32-bit integer number from -2,147,483,648 to 2,147,483,647
uint	System.UInt32	32	Unsigned 32-bit integer number from 0 to 4,294,967,295
long	System.Int64	64	Signed 64-bit integer number from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong	System.UInt64	64	Unsigned 64-bit integer number from 0 to 18,446,744,073,709,551,615
short	System.Int16	16	Signed 16-bit integer number from -32,768 to 32,767
ushort	System.UInt16	16	Unsigned 16-bit integer number from 0 to 65,535

To declare a variable of a predefined type, you can either use the C# type or the .NET Framework type. For example, to declare an integer variable, you can either use the int or System.Int32 type, as shown here:

int num1 = 5;
//---or---
System.Int32 num2 = 5;

To get the type of a variable, use the GetType() method:

Console.WriteLine(num1.GetType()); //---System.Int32---

To get the .NET equivalent of a C# type, use the typeof() method. For example, to learn the .NET type equivalent of C#'s float type, you can use the following statements:

Type t = typeof(float);
Console.WriteLine(t.ToString()); //---System.Single---

To get the size of a type, use the sizeof() method:

Console.WriteLine('{0} bytes', sizeof(int)); //---4 bytes---

In C#, all noninteger numbers are always treated as a double. And so if you want to assign a noninteger number like 3.99 to a float variable, you need to append it with the F (or f) suffix, like this:

float price = 3.99F;

If you don't do this, the compiler will issue an error message: 'Literal of type double cannot be implicitly converted to type 'float'; use an 'F' suffix to create a literal of this type.'

Likewise, to assign a noninteger number to a decimal variable, you need to use the M suffix:

decimal d = 4.56M; //---suffix M to convert to decimal---
float f = 1.23F; //---suffix F to convert to float---

You can also assign integer values using hexadecimal representation. Simply prefix the hexadecimal number with 0x, like this:

int num1 = 0xA;
Console.WriteLine(num1); //---10---

Nullable Type

All value types in C# have a default value when they are declared. For example, the following declaration declares a Boolean and an int variable:

Boolean married; //---default value is false---
int age; //--- default value is 0---

To learn the default value of a value type, use the default keyword, like this:

object x; x = default(int);
Console.WriteLine(x); //---0---
x = default(bool);
Console.WriteLine(x); //---false---

However, C# forbids you from using a variable if you do not explicitly initialize it. The following statements, for instance, cause the compiler to complain:

Boolean married;
//---error: Use of unassigned local variable 'married'---
Console.WriteLine(married);

To use the variable, you first need to initialize it with a value:

Boolean married = false;