Types in C# and the .NET framework are the fundamental building block of program design, and in C# they are divided into built-in, primitive types, and user-defined types. Generally speaking the user-defined types refer to classes, and classes are essentially made up of built-in types and other user-defined types themselves. Primitive types can also be seen as value types, that is a type that has a value in memory, usually called the stack. This is in contrast to reference types that are on the heap, but actually have pointers to themselves on the stack. C# offers the following built-in types:

• Byte
• Char
• Int16
• UInt16
• Int32
• UInt32
• Long
• ULong
• Short
• UShort
• Decimal
• Double
• Float
• SByte
• Single
• Boolean
• Int64
• UInt64