Convert a positive number to negative in C

Question

You can convert a negative number to positive like this   int myInt   System Math Abs -5     Is there an equivalent method to make a positive number negative

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Note to everyone who responded with   - Math Abs myInteger    or   0 - Math Abs myInteger    or  Math Abs myInteger    -1   as a way to keep negative numbers negative and turn positive ones negative   This approach has a single flaw  It doesn t work for all integers  The range of Int32 type is from  -231  to  231 - 1   It means there s one more  negative  number  Consequently  Math Abs int MinValue  throws an OverflowException    The correct way is to use conditional statements   int neg   n  lt  0   n   -n    This approach works for  all  integers

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Even though I m way late to the party here  I m going to chime in with some useful tricks from my hardware days  All of these assume 2 s compliment representation for signed numbers   int negate    i 1  int positiveMagnitude    i    i gt  gt 31   -  i gt  gt 31   int negativeMagnitude    i gt  gt 31  -  i    i gt  gt 31

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Just something that I want to share   public decimal NumberReevaluate decimal number  bool isPositive        var tempNumber   System Math Abs number       return isPositive   tempNumber   -tempNumber

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int myInt   - System Math Abs -5

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I use myInt   -myInt   So simple and easy  If you want to have only positive  myInt   myInt gt 0   myInt   -myInt

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Just for fun   int negativeInt   int Parse String Format   0  1          -   positiveInt ToString        Update   the beauty of this approach is that you can easily refactor it into an exception generator   int negativeInt   int Parse String Format   0  1          thisisthedumbestquestioninstackoverflowhistory   positiveInt ToString

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How about  myInt   myInt   -1

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EDIT   This is wrong for positive inputs    I made mistake of forgetting that the rest of the bits in -x  2s-Complement value   are the  opposite  of their value in  x  not the same   SO simply changing the sign bit will NOT work for positive numbers     I ll leave this here for in for purposes      Or the tricky way   I think       int y   x    int MaxValue   cause int MaxValue is 0111 1111 1111 1111 1111 1111 1111 1111   so    int MaxValue is      1000 0000 0000 0000 0000 0000 0000 0000   and therefore any int32 Or ed with that will put a 1 in the sign bit   making it negative   and leave all the other bits the same      EDIT    actually   Since the 1000 0000 0000 0000 0000 0000 0000 0000 is actually the Minvalue  this should also work      int y   x   int MinValue     or  to do it to itself     x    int MinValue

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X  -1 may not work on all compilers    since it reads a  multiply   SUBTRACT  1 instead of NEGATIVE The better alt is X  0-X    WHICH IS DIFF FROM X- X

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The same way you make anything else negative  put a negative sign in front of it   var positive   6  var negative   -positive

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Use binary and to remove the last bit which is responsible for negative sign   Or use binary or to add sign to a datatype   This soln may sound absurd and incomplete but I can guarantee this is the fastest method   If you don t experiment with what I have posted this post may look crap  D  Eg for int   Int is 32 bit datatype so the last bit  32th one  determines the sign   And with a value which has 0 in the 32 place and rest 1  It will convert negative no to  ve   For just the opposite or with a value with 1 in 32th place and rest 0

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int myNegInt   System Math Abs myNumber     -1

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To switch the sign of an integer  you just use the sign operator   myInt   -myInt    To make it negative regardless if the original value is negative or not  you first use the Abs method   myInt   -Math Abs myInt

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The easy way   myInt    -1

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int negInt   0 - myInt    Or guaranteed to be negative   int negInt   -System Math Abs someInt

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Maybe this   int n        some coding      n   n lt  0  n 0-n

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Just for more fun   int myInt   Math Min hisInt  -hisInt    int myInt   - int Math Sqrt Math Pow Math Sin 1   2    Math Pow Math Cos -1   2                 Math Abs hisInt

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long negativeNumber    long positiveInt -  long  int MaxValue   1     Nobody said it had to be any particular negative number

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As previously mentioned  just multiplying by -1 is not cool  as int MinValue   -1    int MinValue It really depends on your application  but for mine  Inverting Joystick axes  I want to ensure that all extremes are still reachable  and maintain as much fidelity as possible  To this end  I map Max  lt -- gt  Min and everything in-between gets a   -1 Using this technique  -32767 is unreachable when inverting      private static int Invert int value                if  value    int MaxValue  return int MinValue          if  value    int MinValue  return int MaxValue          return value   -1

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int negInt   -System Math Abs myInt

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Converting a number from positive to negative  or negative to positive   public static decimal Reverse this decimal source         return source   decimal MinusOne

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Multiply it by -1

[c#] Convert a positive number to negative in C#

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