decimal vs double - Which one should I use and when

Question

I keep seeing people using doubles in C   I know I read somewhere that doubles sometimes lose precision   My question is when should a use a double and when should I use a decimal type  Which type is suitable for money computations   ie  greater than  100 million

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Decimal is for exact values  Double is for approximate values   USD   12 345 67 USD  Decimal  CAD   13 617 27  Decimal  Exchange Rate  1 102932  Double

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For money  decimal  It costs a little more memory  but doesn t have rounding troubles like double sometimes has

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My question is when should a use a   double and when should I use a decimal   type    decimal for when you work with values in the range of 10    -28  and where you have expectations about the behaviour based on base 10 representations - basically money   double for when you need relative accuracy  i e  losing precision in the trailing digits on large values is not a problem  across wildly different magnitudes - double covers more than 10    -300   Scientific calculations are the best example here      which type is suitable for money   computations    decimal  decimal  decimal  Accept no substitutes   The most important factor is that double  being implemented as a binary fraction  cannot accurately represent many decimal fractions  like 0 1  at all and its overall number of digits is smaller since it is 64-bit wide vs  128-bit for decimal  Finally  financial applications often have to follow specific rounding modes  sometimes mandated by law   decimal supports these  double does not

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Definitely use integer types for your money computations  This cannot be emphasized enough since at first glance it might seem that a floating point type is adequate    Here an example in python code    gt  gt  gt  amount   float 100 00    one hundred dollars  gt  gt  gt  print amount 100 0  gt  gt  gt  new amount   amount   1  gt  gt  gt  print new amount 101 0  gt  gt  gt  print new amount - amount  gt  gt  gt  1 0   looks pretty normal    Now try this again with 10 20 Zimbabwe dollars    gt  gt  gt  amount   float 1e20   gt  gt  gt  print amount 1e 20  gt  gt  gt  new amount   amount   1  gt  gt  gt  print new amount 1e 20  gt  gt  gt  print new amount-amount 0 0   As you can see  the dollar disappeared    If you use the integer type  it works fine    gt  gt  gt  amount   int 1e20   gt  gt  gt  print amount 100000000000000000000  gt  gt  gt  new amount   amount   1  gt  gt  gt  print new amount 100000000000000000001  gt  gt  gt  print new amount - amount 1

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For money  always decimal  It s why it was created   If numbers must add up correctly or balance  use decimal  This includes any financial storage or calculations  scores  or other numbers that people might do by hand   If the exact value of numbers is not important  use double for speed  This includes graphics  physics or other physical sciences computations where there is already a  number of significant digits

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I think that the main difference beside bit width is that decimal has exponent base 10 and double has 2  http   software-product-development blogspot com 2008 07 net-double-vs-decimal html

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System Single   float - 7 digits System Double   double - 15-16 digits System Decimal   decimal - 28-29 significant digits  The way I ve been stung by using the wrong type  a good few years ago  is with large amounts      520 532 52 - 8 digits     1 323 523 12 - 9 digits   You run out at 1 million for a float   A 15 digit monetary value      1 234 567 890 123 45   9 trillion with a double  But with division and comparisons it s more complicated  I m definitely no expert in floating point and irrational numbers - see Marc s point   Mixing decimals and doubles causes issues      A mathematical or comparison operation   that uses a floating-point number   might not yield the same result if a   decimal number is used because the   floating-point number might not   exactly approximate the decimal   number    When should I use double instead of decimal  has some similar and more in depth answers    Using double instead of decimal for monetary applications is a micro-optimization - that s the simplest way I look at it

[c#] decimal vs double! - Which one should I use and when?

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