C# includes a number of pre-defined “built-in” data types. Each built-in data type is represented by a class in the System namespace that inherits from the base System.Object class. For example, an integer is represented by the System.Int32 class, and a string is represented by the System.String class.
C# defines an alias keyword for each built-in type. The alias keyword and its corresponding C# type are interchangeable. For example, you can define a string with the “string” keyword or “System.String” type:
string s1 = "Hello"; System.String s2 = "World";
The following table shows the built-in C# types, their alias keywords and corresponding C# type:
C# Built-In Type .NET Framework Type bool System.Boolean byte System.Byte char System.Char decimal System.Decimal double System.Double float System.Single int System.Int32 long System.Int64 object System.Object sbyte System.SByte short System.Int16 string System.String uint System.UInt32 ulong System.UInt64 ushort System.UInt16