int to unsigned int conversion

Question

I m just amazed to know that I can t convert signed to unsigned int by casting   int i   -62  unsigned int j    unsigned int i    I thought I already knew this since I started to use casts  but I can t do it

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with a little help of math   include  lt math h gt  int main      int a   -1    unsigned int b    b   abs a

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You can convert an int to an unsigned int   The conversion is valid and well-defined   Since the value is negative  UINT MAX   1 is added to it so that the value is a valid unsigned quantity    Technically  2N is added to it  where N is the number of bits used to represent the unsigned type     In this case  since int on your platform has a width of 32 bits  62 is subtracted from 232  yielding 4 294 967 234

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Edit  As has been noted in the other answers  the standard actually guarantees that  the resulting value is the least unsigned integer congruent to the source integer  modulo 2n where n is the number of bits used to represent the unsigned type    So even if your platform did not store signed ints as two s complement  the behavior would be the same     Apparently your signed integer -62 is stored in two s complement  Wikipedia  on your platform   62 as a 32-bit integer written in binary is  0000 0000 0000 0000 0000 0000 0011 1110   To compute the two s complement  for storing -62   first invert all the bits  1111 1111 1111 1111 1111 1111 1100 0001   then add one  1111 1111 1111 1111 1111 1111 1100 0010   And if you interpret this as an unsigned 32-bit integer  as your computer will do if you cast it   you ll end up with 4294967234  -

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i -62   If you want to convert it to a unsigned representation  It would be 4294967234 for a 32 bit integer   A simple way would be to  num -62 unsigned int n  n   num cout lt  lt n       4294967234

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Since we know that i is an int  you can just go ahead and unsigneding it   This would do the trick   int i   -62  unsigned int j   unsigned i

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This conversion is well defined and will yield the value UINT MAX - 61   On a platform where unsigned int is a 32-bit type  most common platforms  these days   this is precisely the value that others are reporting   Other values are possible  however   The actual language in the standard is      If the destination type is unsigned    the resulting value is the least   unsigned integer congruent to the   source integer  modulo 2 n where n is   the number of bits used to represent   the unsigned type

[c++] int to unsigned int conversion

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