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c# 의 data type 과 mssql 의 data type 데이터타입 비교 본문

닷넷관련/CSharp

c# 의 data type 과 mssql 의 data type 데이터타입 비교

재우니 2019. 11. 20. 17:34

https://www.tutorialsteacher.com/csharp/csharp-data-types

 

Data types in C#

C# - Data Types C# is a strongly-typed language. It means we must declare the type of a variable which indicates the kind of values it is going to store such as integer, float, decimal, text, etc. The following declares and initialized variables of differe

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string stringVar = "Hello World!!";
int intVar = 100;
float floatVar = 10.2f;
char charVar = 'A';
bool boolVar = true;

C# - Data Types

C# is a strongly-typed language. It means we must declare the type of a variable which indicates the kind of values it is going to store such as integer, float, decimal, text, etc.

The following declares and initialized variables of different data types.

Example: Variables of Different Data Types

 

Try it

C# mainly categorized data types in two types: Value types and Reference types. Value types include simple types (e.g. int, float, bool, and char), enum types, struct types, and Nullable value types. Reference types include class types, interface types, delegate types, and array types. Learn about value types and reference types in detail in the next chapter.

Predefined Data Types in C#

C# includes some predefined value types and reference types. The following table lists predefined data types:

TypeDescriptionRangeSuffix

byte 8-bit unsigned integer 0 to 255
sbyte 8-bit signed integer -128 to 127
short 16-bit signed integer -32,768 to 32,767
ushort 16-bit unsigned integer 0 to 65,535
int 32-bit signed integer -2,147,483,648
to
2,147,483,647
uint 32-bit unsigned integer 0 to 4,294,967,295 u
long 64-bit signed integer -9,223,372,036,854,775,808
to
9,223,372,036,854,775,807
l
ulong 64-bit unsigned integer 0 to 18,446,744,073,709,551,615 ul
float 32-bit Single-precision floating point type -3.402823e38 to 3.402823e38 f
double 64-bit double-precision floating point type -1.79769313486232e308 to 1.79769313486232e308 d
decimal 128-bit decimal type for financial and monetary calculations (+ or -)1.0 x 10e-28
to
7.9 x 10e28
m
char 16-bit single Unicode character Any valid character, e.g. a,*, \x0058 (hex), or\u0058 (Unicode)
bool 8-bit logical true/false value True or False
object Base type of all other types.
string A sequence of Unicode characters
DateTime Represents date and time 0:00:00am 1/1/01
to
11:59:59pm 12/31/9999

As you can see in the above table that each data types (except string and object) includes value range. Compiler will give an error if value goes out of datatype's permitted range. For example, int data type's range is -2,147,483,648 to 2,147,483,647. So if you assign value which is not in this range then compiler would give error.

Example: Compile time error

// compile time error: Cannot implicitly convert type 'long' to 'int'.
int i = 21474836470; 

The value of unsigned integers, long, float, double, and decimal type must be suffix by u,l,f,d, and m respectively.

Example: Value Suffix

uint ui = 100u;
float fl = 10.2f;
long l = 45755452222222l;
ulong ul = 45755452222222ul;
double d = 11452222.555d;
decimal mon = 1000.15m;

Try it

Alias vs .Net Type

The above table of predefined data types are actually alias to their .NET type (CLR class) name. The following table lists alias for predefined data types and related .NET class name.

Alias.NET TypeType

byte System.Byte struct
sbyte System.SByte struct
int System.Int32 struct
uint System.UInt32 struct
short System.Int16 struct
ushort System.UInt16 struct
long System.Int64 struct
ulong System.UInt64 struct
float System.Single struct
double System.Double struct
char System.Char struct
bool System.Boolean struct
object System.Object Class
string System.String Class
decimal System.Decimal struct
DateTime System.DateTime struct

It means that whether you define a variable of int or Int32, both are same.

int i = 345;
Int32 i = 345;// same as above 

Default Value

Every data type has a default value. Numeric type is 0, boolean has false and char has '/0' as default value. Use default(typename) to assign a default value of the data type or C# 7.1 onward, use default literal.

int i = default(int); // 0
float f = default(float);// 0
decimal d = default(decimal);// 0
bool b = default(bool);// false
char c = default(char);// '\0'

// C# 7.1 onwards
int i = default; // 0
float f = default;// 0
decimal d = default;// 0
bool b = default;// false
char c = default;// '\0'

Conversion

The values of certain data types are automatically converted to the different data types in C#. This is called implicit conversion.

Example: Implicit Conversion

int i = 345;
float f = i;

Console.WriteLine(f); //output: 345

In the above example, value of an integer variable i is assigned to the variable of float type f because this conversion operation is predefined in C#.

The following is an implicit data types conversion table.

Implicit Conversion FromTo

sbyte short, int, long, float, double, decimal
byte short, ushort, int, uint, long, ulong, float, double, decimal
short int, long, float, double, or decimal
ushort int, uint, long, ulong, float, double, or decimal
int long, float, double, or decimal.
uint long, ulong, float, double, or decimal
long float, double, or decimal
ulong float, double, or decimal
char ushort, int, uint, long, ulong, float, double, or decimal
float Double

Conversions from int, uint, long, or ulong to float and from long or ulong to double may cause a loss of precision. No data type implicitly converted to the char type.

However, not all data types are implicitly converted to other data types. For example, int type cannot be converted to uint implicitly, it must be specify explicitly, as shown below.

Example: Explicit Conversion

public static void Main()
{
    int i = 100;
    uint u = (uint) i;
    Console.Write(i);
}

In the above example, integer i is converted to uint explicitly by specifying uint in the brackets (uint). This will convert an integer to uint.

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