Built-in Types

In C#, built-in types are the primitive data types that the C# language provides out-of-the-box. They are really just aliases for .NET Framework types in the System namespace, but the C# keywords make them easier to use.

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📌 1. Categories of Built-in Types

Integral Types

• Whole numbers (signed and unsigned).

C# Keyword	.NET Type	Size	Range
sbyte	System.SByte	8-bit	-128 to 127
byte	System.Byte	8-bit	0 to 255
short	System.Int16	16-bit	-32,768 to 32,767
ushort	System.UInt16	16-bit	0 to 65,535
int	System.Int32	32-bit	-2,147,483,648 to 2,147,483,647
uint	System.UInt32	32-bit	0 to 4,294,967,295
long	System.Int64	64-bit	-9.22e18 to 9.22e18
ulong	System.UInt64	64-bit	0 to 1.84e19
char	System.Char	16-bit	Single Unicode character

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Floating-point & Decimal Types

• For real numbers and precise decimal calculations.

C# Keyword	.NET Type	Size	Range / Precision
float	System.Single	32-bit	~7 digits of precision
double	System.Double	64-bit	~15–16 digits of precision
decimal	System.Decimal	128-bit	28–29 significant digits (great for money)

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Other Primitive Types

C# Keyword	.NET Type	Description
bool	System.Boolean	Represents true or false.
string	System.String	Immutable sequence of characters.
object	System.Object	Base type for all types in C#.
dynamic	System.Object	Runtime-typed object (late binding).

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Special Types

C# Keyword	.NET Type	Description
void	N/A	Represents no return value (used in methods).
var	Compiler-inferred	Type inferred at compile time.
null	Literal	Represents “no value” for reference types.

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📌 2. Example Usage

class Program
{
    static void Main()
    {
        int age = 25;
        double pi = 3.14159;
        decimal money = 19.99m;
        char grade = 'A';
        bool isActive = true;
        string name = "Alice";
 
        Console.WriteLine($"{name}, {age} years old, Grade: {grade}, Active: {isActive}, Balance: {money}, Pi: {pi}");
    }
}

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📌 3. Key Notes

• Aliases vs .NET types:
  int ↔ System.Int32, string ↔ System.String.
  Both are the same, but C# developers almost always use the keyword.

• Value types vs Reference types:

  • Value types: numbers, bool, struct, enum → stored on the stack.

  • Reference types: string, object, dynamic, arrays, classes → stored on the heap.

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✅ Summary:

• Built-in types = C# keywords (aliases) for System types.

• Categories: integral, floating-point, decimal, boolean, char, string, object, dynamic, void.

• They’re the foundation of all data handling in C#.