Difference between decimal float and double in NET

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What is the difference between decimal  float and double in  NET   When would someone use one of these

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--------- ---------------- --------- ---------- ---------------------------------------------------------    C          Net Framework   Signed    Bytes      Possible Values                                             Type       System  type              Occupied                                                              --------- ---------------- --------- ---------- ---------------------------------------------------------    sbyte     System Sbyte     Yes       1          -128 to 127                                                 short     System Int16     Yes       2          -32 768 to 32 767                                           int       System Int32     Yes       4          -2 147 483 648 to 2 147 483 647                             long      System Int64     Yes       8          -9 223 372 036 854 775 808 to 9 223 372 036 854 775 807     byte      System Byte      No        1          0 to 255                                                    ushort    System Uint16    No        2          0 to 65 535                                                 uint      System UInt32    No        4          0 to 4 294 967 295                                          ulong     System Uint64    No        8          0 to 18 446 744 073 709 551 615                             float     System Single    Yes       4          Approximately   1 5e-45 to   3 4e38                                                                            with  6-9 significant figures                              double    System Double    Yes       8          Approximately   5 0e-324 to   1 7e308                                                                          with  15-17 significant figures                            decimal   System Decimal   Yes       16         Approximately   1 0e-28 to   7 9e28                                                                            with 28-29 significant figures                             char      System Char      N A       2          Any Unicode character  16 bit                               bool      System Boolean   N A       1   2      true or false                                              --------- ---------------- --------- ---------- ---------------------------------------------------------   See here for more information

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The Decimal structure is strictly geared to financial calculations requiring accuracy  which are relatively intolerant of rounding   Decimals are not adequate for scientific applications  however  for several reasons    A certain loss of precision is acceptable in many scientific calculations because of the practical limits of the physical problem or artifact being measured   Loss of precision is not acceptable in finance  Decimal is much  much  slower than float and double for most operations  primarily because floating point operations are done in binary  whereas Decimal stuff is done in base 10  i e  floats and doubles are handled by the FPU hardware  such as MMX SSE  whereas decimals are calculated in software   Decimal has an unacceptably smaller value range than double  despite the fact that it supports more digits of precision  Therefore  Decimal can t be used to represent many scientific values

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The problem with all these types is that a certain imprecision subsists  AND that this problem can occur with small decimal numbers like in the following example  Dim fMean as Double   1 18 Dim fDelta as Double   0 08 Dim fLimit as Double   1 1  If fMean - fDelta  lt  fLimit Then     bLower   True Else     bLower   False End If   Question  Which value does bLower variable contain    Answer  On a 32 bit machine bLower contains TRUE      If I replace Double by Decimal  bLower contains FALSE which is the good answer   In double  the problem is that fMean-fDelta   1 09999999999 that is lower that 1 1   Caution  I think that same problem can certainly exists for other number because Decimal is only a double with higher precision and the precision has always a limit   In fact  Double  Float and Decimal correspond to BINARY decimal in COBOL    It is regrettable that other numeric types implemented in COBOL don t exist in  Net  For those that don t know COBOL  there exist in COBOL following numeric type  BINARY or COMP like float or double or decimal PACKED-DECIMAL or COMP-3  2 digit in 1 byte  ZONED-DECIMAL  1 digit in 1 byte

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To define Decimal  Float and Double in  Net  c   you must mention values as  Decimal dec   12M 6  Double dbl   11D 6  float fl   15F 6   and check the results  And Bytes Occupied by each are Float - 4 Double - 8 Decimal - 12

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The Decimal  Double  and Float variable types are different in the way that they store the values  Precision is the main difference where float is a single precision  32 bit  floating point data type  double is a double precision  64 bit  floating point data type and decimal is a 128-bit floating point data type   Float - 32 bit  7 digits   Double - 64 bit  15-16 digits   Decimal - 128 bit  28-29 significant digits   More about   the difference between Decimal  Float and Double

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In simple words      The Decimal  Double  and Float variable types are different in the way that they store the values   Precision is the main difference  Notice that this is not the single difference  where float is a single precision  32 bit  floating point data type  double is a double precision  64 bit  floating point data type and decimal is a 128-bit floating point data type  The summary table                                                                                                    Type       Bits    Have up to                   Approximate Range                                                                                                  float      32      7 digits                     -3 4    10    38    to  3 4    10    38      double     64      15-16 digits                   5 0    10    -324  to   1 7    10    308      decimal    128     28-29 significant digits       7 9 x 10    28  or  1 to 10    28                                                                                               You can read more here  Float  Double  and Decimal

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I won t reiterate tons of good  and some bad  information already answered in other answers and comments  but I will answer your followup question with a tip      When would someone use one of these    Use decimal for counted values  Use float double for measured values  Some examples    money  do we count money or measure money   distance  do we count distance or measure distance     scores  do we count scores or measure scores     We always count money and should never measure it  We usually measure distance  We often count scores     In some cases  what I would call nominal distance  we may indeed want to  count  distance  For example  maybe we are dealing with country signs that show distances to cities  and we know that those distances never have more than one decimal digit  xxx x km

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This has been an interesting thread for me  as today  we ve just had a nasty little bug  concerning decimal having less precision than a float   In our C  code  we are reading numeric values from an Excel spreadsheet  converting them into a decimal  then sending this decimal back to a Service to save into a SQL Server database   Microsoft Office Interop Excel Range cell       object cellValue   cell Value2  if  cellValue    null        decimal value   0      Decimal TryParse cellValue ToString    out value       Now  for almost all of our Excel values  this worked beautifully  But for some  very small Excel values  using decimal TryParse lost the value completely  One such example is   cellValue   0 00006317592 Decimal TryParse cellValue ToString    out value      would return 0   The solution  bizarrely  was to convert the Excel values into a double first  and then into a decimal   Microsoft Office Interop Excel Range cell       object cellValue   cell Value2  if  cellValue    null        double valueDouble   0      double TryParse cellValue ToString    out valueDouble       decimal value    decimal  valueDouble              Even though double has less precision than a decimal  this actually ensured small numbers would still be recognised  For some reason  double TryParse was actually able to retrieve such small numbers  whereas decimal TryParse would set them to zero   Odd  Very odd

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Decimal 128 bit  28-29 significant digits  In case of financial applications it is better to use  Decimal types because it gives you a high level of accuracy and easy to avoid rounding errors Use decimal for non-integer math where precision is needed  e g  money and currency  Double  64 bit  15-16 digits  Double Types are probably the most normally used data type for real values  except handling money  Use double for non-integer math where the most precise answer isn t necessary  Float  32 bit  7 digits  It is used mostly in graphic libraries because very high demands for processing powers  also used situations that can endure rounding errors    Decimals are much slower than a double float    Decimals and Floats Doubles cannot be compared without a cast whereas Floats and Doubles can    Decimals also allow the encoding or trailing zeros

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No one has mentioned that     In default settings  Floats  System Single  and doubles  System Double  will never use   overflow checking while Decimal  System Decimal  will always use   overflow checking    I mean   decimal myNumber   decimal MaxValue  myNumber    1    throws OverflowException   But these do not   float myNumber   float MaxValue  myNumber    1     amp   double myNumber   double MaxValue  myNumber    1

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float and double are floating binary point types  In other words  they represent a number like this   10001 10010110011   The binary number and the location of the binary point are both encoded within the value   decimal is a floating decimal point type  In other words  they represent a number like this   12345 65789   Again  the number and the location of the decimal point are both encoded within the value     that s what makes decimal still a floating point type instead of a fixed point type   The important thing to note is that humans are used to representing non-integers in a decimal form  and expect exact results in decimal representations  not all decimal numbers are exactly representable in binary floating point     0 1  for example     so if you use a binary floating point value you ll actually get an approximation to 0 1  You ll still get approximations when using a floating decimal point as well     the result of dividing 1 by 3 can t be exactly represented  for example   As for what to use when    For values which are  naturally exact decimals  it s good to use decimal  This is usually suitable for any concepts invented by humans  financial values are the most obvious example  but there are others too  Consider the score given to divers or ice skaters  for example  For values which are more artefacts of nature which can t really be measured exactly anyway  float double are more appropriate  For example  scientific data would usually be represented in this form  Here  the original values won t be  decimally accurate  to start with  so it s not important for the expected results to maintain the  decimal accuracy   Floating binary point types are much faster to work with than decimals

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For applications such as games and embedded systems where memory and performance are both critical  float is usually the numeric type of choice as it is faster and half the size of a double  Integers used to be the weapon of choice  but floating point performance has overtaken integer in modern processors  Decimal is right out

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float    1 5 x 10 -45 to   3 4 x 10 38   7 significant figures double    5 0 x 10 -324 to   1 7 x 10 308  15-16 significant figures  decimal    1 0 x 10 -28 to   7 9 x 10 28  28-29 significant figures

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Integers  as was mentioned  are whole numbers  They can t store the point something  like  7   42  and  007  If you need to store numbers that are not whole numbers  you need a different type of variable  You can use the double type or the float type  You set these types of variables up in exactly the same way  instead of using the word int  you type double or float  Like this   float myFloat  double myDouble     float is short for  floating point   and just means a number with a point something on the end    The difference between the two is in the size of the numbers that they can hold  For float  you can have up to 7 digits in your number  For doubles  you can have up to 16 digits  To be more precise  here s the official size   float   1 5    10 -45  to 3 4    10 38   double  5 0    10 -324 to 1 7    10 308   float is a 32-bit number  and double is a 64-bit number   Double click your new button to get at the code  Add the following three lines to your button code   double myDouble  myDouble   0 007  MessageBox Show myDouble ToString       Halt your program and return to the coding window  Change this line   myDouble   0 007  myDouble   12345678 1234567    Run your programme and click your double button  The message box correctly displays the number  Add another number on the end  though  and C  will again round up or down  The moral is if you want accuracy  be careful of rounding

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Precision is the main difference    Float - 7 digits  32 bit   Double-15-16 digits  64 bit   Decimal -28-29 significant digits  128 bit   Decimals have much higher precision and are usually used within financial applications that require a high degree of accuracy  Decimals are much slower  up to 20X times in some tests  than a double float    Decimals and Floats Doubles cannot be compared without a cast whereas Floats and Doubles can  Decimals also allow the encoding or trailing zeros   float flt   1F 3  double dbl   1D 3  decimal dcm   1M 3  Console WriteLine  float   0  double   1  decimal   2    flt  dbl  dcm     Result     float  0 3333333   double  0 333333333333333   decimal  0 3333333333333333333333333333

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Double and float can be divided by integer zero without an exception at both compilation and run time  Decimal cannot be divided by integer zero  Compilation will always fail if you do that

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The main difference between each of these is the precision   float is a 32-bit number  double is a 64-bit number and decimal is a 128-bit number

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float 7 digits of precision   double has about 15 digits of precision  decimal has about 28 digits of precision  If you need better accuracy  use double instead of float  In modern CPUs both data types have almost the same performance  The only benifit of using float is they take up less space  Practically matters only if you have got many of them   I found this is interesting  What Every Computer Scientist Should Know About Floating-Point Arithmetic

[.net] Difference between decimal, float and double in .NET?

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