What is a difference between unsigned int and signed int in C

Question

Consider these definitions   int x 5  int y -5  unsigned int z 5    How are they stored in memory  Can anybody explain the bit representation of these in memory   Can int x 5 and int y -5 have same bit representation in memory

User · Answer

Assuming int is a 16 bit integer  which depends on the C implementation  most are 32 bit nowadays  the bit representation differs like the following    5   0000000000000101 -5   1111111111111011   if binary 1111111111111011 would be set to an unsigned int  it would be decimal 65531

User · Answer

Because it s all just about memory  in the end all the numerical values are stored in binary   A 32 bit unsigned integer can contain values from all binary 0s to all binary 1s   When it comes to 32 bit signed integer  it means one of its bits  most significant  is a flag  which marks the value to be positive or negative

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The C standard specifies that unsigned numbers will be stored in binary   With optional padding bits   Signed numbers can be stored in one of three formats  Magnitude and sign  two s complement or one s complement  Interestingly that rules out certain other representations like Excess-n or Base -2   However on most machines and compilers store signed numbers in 2 s complement   int is normally 16 or 32 bits  The standard says that  int should be whatever is most efficient for the underlying processor  as long as it is  gt   short and  lt   long then it is allowed by the standard   On some machines and OSs history has causes int not to be the best size for the current iteration of hardware however

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ISO C states what the differences are   The int data type is signed and has a minimum range of at least -32767 through 32767 inclusive  The actual values are given in limits h as INT MIN and INT MAX respectively   An unsigned int has a minimal range of 0 through 65535 inclusive with the actual maximum value being UINT MAX from that same header file   Beyond that  the standard does not mandate twos complement notation for encoding the values  that s just one of the possibilities  The three allowed types would have encodings of the following for 5 and -5  using 16-bit data types            two s complement     ones  complement       sign magnitude      --------------------- --------------------- ---------------------   5    0000 0000 0000 0101   0000 0000 0000 0101   0000 0000 0000 0101   -5    1111 1111 1111 1011   1111 1111 1111 1010   1000 0000 0000 0101        --------------------- --------------------- ---------------------     In two s complement  you get a negative of a number by inverting all bits then adding 1  In ones  complement  you get a negative of a number by inverting all bits  In sign magnitude  the top bit is the sign so you just invert that to get the negative    Note that positive values have the same encoding for all representations  only the negative values are different   Note further that  for unsigned values  you do not need to use one of the bits for a sign  That means you get more range on the positive side  at the cost of no negative encodings  of course    And no  5 and -5 cannot have the same encoding regardless of which representation you use  Otherwise  there d be no way to tell the difference     As an aside  there are currently moves underway  in both C and C   standards  to nominate two s complement as the only encoding for negative integers

User · Answer

Here is the very nice link which explains the storage of signed and unsigned INT in C -  http   answers yahoo com question index qid 20090516032239AAzcX1O  Taken from this above article -   process called two s complement is used to transform positive numbers into negative numbers  The side effect of this is that the most significant bit is used to tell the computer if the number is positive or negative  If the most significant bit is a 1  then the number is negative  If it s 0  the number is positive

[c] What is a difference between unsigned int and signed int in C?

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