How to determine if a decimal double is an integer

Question

How do I tell if a decimal or double value is an integer   For example   decimal d   5 0     Would be true decimal f   5 5     Would be false   or   double d   5 0     Would be true double f   5 5     Would be false   The reason I would like to know this is so that I can determine programmatically if I want to output the value using  ToString  N0   or  ToString  N2     If there is no decimal point value  then I don t want to show that

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I faced a similar situation  but where the value is a string  The user types in a value that s supposed to be a dollar amount  so I want to validate that it s numeric and has at most two decimal places   Here s my code to return true if the string  s  represents a numeric with at most two decimal places  and false otherwise  It avoids any problems that would result from the imprecision of floating-point values   try          must be numeric value     double d   double Parse s          max of two decimal places     if  s IndexOf       gt   0                if  s Length  gt  s IndexOf        3              return false            return true  catch       return false      I discuss this in more detail at http   progblog10 blogspot com 2011 04 determining-whether-numeric-value-has html

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public static bool isInteger decimal n                return n -  Int64 n    0

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Perhaps not the most elegant solution but it works if you are not too picky   bool IsInteger double num        return  num ToString  0                    Contains

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There are any number of ways to do this   For example   double d   5 0  bool isInt   d     int d    You can also use modulo   double d   5 0  bool isInt   d   1    0

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static bool IsWholeNumber double x         return Math Abs x   1   lt  double Epsilon

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If upper and lower bound of Int32 matters   public bool IsInt32 double value        return  value  gt   int MinValue  amp  amp  value  lt   int MaxValue  amp  amp  value     int value

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Mark Rushakoff s answer may be simpler  but the following also work and may be more efficient since there is no implicit division operation        bool isInteger    double   int f     f     and       bool isInteger    decimal   int d     d     If you want a single expression for both types  perhaps       bool isInteger    double   int val      double val

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Using int TryParse will yield these results           var shouldBeInt   3           var shouldntBeInt   3 1415           var iDontWantThisToBeInt   3 000f           Console WriteLine int TryParse shouldBeInt ToString    out int parser       true          Console WriteLine int TryParse shouldntBeInt ToString    out parser       false          Console WriteLine int TryParse iDontWantThisToBeInt ToString    out parser       true  even if I don t want this to be int          Console WriteLine int TryParse  3 1415   out  parser       false          Console WriteLine int TryParse  3 0000   out parser       false          Console WriteLine int TryParse  3   out parser       true          Console ReadKey

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Whilst the solutions proposed appear to work for simple examples  doing this in general is a bad idea  A number might not be exactly an integer but when you try to format it  it s close enough to an integer that you get 1 000000  This can happen if you do a calculation that in theory should give exactly 1  but in practice gives a number very close to but not exactly equal to one due to rounding errors   Instead  format it first and if your string ends in a period followed by zeros then strip them  There are also some formats that you can use that strip trailing zeros automatically  This might be good enough for your purpose   double d   1 0002  Console WriteLine d ToString  0        d   1 02  Console WriteLine d ToString  0          Output   1 1 02

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You can use String formatting for the double type  Here is an example   double val   58 6547  String Format   0 0       val           Output   58 65   double val   58 6  String Format   0 0       val           Output   58 6   double val   58 0  String Format   0 0       val           Output   58    Let me know if this doesn t help

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Try this   number    Convert ToInt16 number

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bool IsInteger double num        if  ceil num     num  amp  amp  floor num     num          return true      else         return false      Problemo solvo   Edit  Pwned by Mark Rushakoff

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How about this   public static bool IsInteger double number        return number    Math Truncate number       Same code for decimal   Mark Byers made a good point  actually  this may not be what you really want  If what you really care about is whether a number rounded to the nearest two decimal places is an integer  you could do this instead   public static bool IsNearlyInteger double number        return Math Round number  2     Math Round number

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For floating point numbers  n   1    0 is typically the way to check if there is anything past the decimal point     public static void Main  string   args        decimal d   3 1M      Console WriteLine  d   1     0       d   3 0M      Console WriteLine  d   1     0       Output   False True   Update  As  Adrian Lopez mentioned below  comparison with a small value epsilon will discard floating-point computation mis-calculations  Since the question is about double values  below will be a more floating-point calculation proof answer   Math Abs d   1   lt    Double Epsilon   100

[c#] How to determine if a decimal/double is an integer?

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