C＃中的浮点数到十进制转换

Question

int i = 1;        // -2,147,483,648 to 2,147,483,647
float f = 2.1f;      // -3.402823e38 to 3.402823e38
long l = 3;       // -922337203685477508 to 922337203685477507
double dbl = 4.5;   // -1.79769313486232e308 to 1.79769313486232e308
decimal dec = 5.2m;  // -79228162514264337593543950335 to 79228162514264337593543950335

dec = i;     // No error
dec = l;     // No error

dec = f;    // Compiler error
dec = dbl;  // Compiler error

f = (float)dec; // No error (May loss precision) ok

**dec = (decimal)dbl;** // No error  why it requires ?  

Why the above code requires Explicit Cast. Range of float/Double > Decimal ?

Answer 1

Because it isn't just about precision; you need to think about range too - and frankly 1.79769313486232e308 is really, really large (as in > 300 digits to the left of the decimal place). Your assertion "Even Range of decimal > float or double" is incorrect.

var dbl = double.MaxValue;
var dec = (decimal) dbl; // BOOM!

The range of a double is larger than the range of a decimal .

Also, you might need to consider double.NaN , double.PositiveInfinity and double.NegativeInfinity .

Answer 2

I believe the Conversion depends on the size of the datatype not on the Range of the Datatype.

Integral Types

DataType    Size    . Net (CTS) Comments
byte    1   System.Byte 0 - 255 It is Unsigned
sbyte   1   System.SByte    -128 to 127 - Signed
short   2   System.Int16    
ushort  2   System.UInt16   
int     4   System.Int32     
uint    4   System.Unt32    
long    8   System.Int64    
ulong   8   System.UInt64   

Floating Types
decimal 16  System.Decimal  Has up to 28 digits after decimal
float   4   System.Single   Has up to 8 digits after decimal
double  8   System.Double   Has up to 15 digits after decimal