What is the difference between signed and unsigned int

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In laymen s terms an unsigned int is an integer that can not be negative and thus has a higher range of positive values that it can assume  A signed int is an integer that can be negative but has a lower positive range in exchange for more negative values it can assume

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Sometimes we know in advance that the value stored in a given integer variable will always be positive-when it is being used to only count things  for example  In such a case we can declare the variable to be unsigned  as in  unsigned int num student   With such a declaration  the range of permissible integer values  for a 32-bit compiler  will shift from the range -2147483648 to  2147483647 to range 0 to 4294967295  Thus  declaring an integer as unsigned almost doubles the size of the largest possible value that it can otherwise hold

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As you are probably aware  ints are stored internally in binary   Typically an int contains 32 bits  but in some environments might contain 16 or 64 bits  or even a different number  usually but not necessarily a power of two    But for this example  let s look at 4-bit integers   Tiny  but useful for illustration purposes   Since there are four bits in such an integer  it can assume one of 16 values  16 is two to the fourth power  or 2 times 2 times 2 times 2   What are those values   The answer depends on whether this integer is a signed int or an unsigned int   With an unsigned int  the value is never negative  there is no sign associated with the value   Here are the 16 possible values of a four-bit unsigned int   bits  value 0000    0 0001    1 0010    2 0011    3 0100    4 0101    5 0110    6 0111    7 1000    8 1001    9 1010   10 1011   11 1100   12 1101   13 1110   14 1111   15       and Here are the 16 possible values of a four-bit signed int   bits  value 0000    0 0001    1 0010    2 0011    3 0100    4 0101    5 0110    6 0111    7 1000   -8 1001   -7 1010   -6 1011   -5 1100   -4 1101   -3 1110   -2 1111   -1   As you can see  for signed ints the most significant bit is 1 if and only if the number is negative   That is why  for signed ints  this bit is known as the  sign bit

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int and unsigned int are two distinct integer types   int can also be referred to as signed int  or just signed  unsigned int can also be referred to as unsigned    As the names imply  int is a signed integer type  and unsigned int is an unsigned integer type  That means that int is able to represent negative values  and unsigned int can represent only non-negative values   The C language imposes some requirements on the ranges of these types  The range of int must be at least -32767     32767  and the range of unsigned int must be at least 0    65535  This implies that both types must be at least 16 bits  They re 32 bits on many systems  or even 64 bits on some  int typically has an extra negative value due to the two s-complement representation used by most modern systems   Perhaps the most important difference is the behavior of signed vs  unsigned arithmetic  For signed int  overflow has undefined behavior  For unsigned int  there is no overflow  any operation that yields a value outside the range of the type wraps around  so for example UINT MAX   1U    0U   Any integer type  either signed or unsigned  models a subrange of the infinite set of mathematical integers  As long as you re working with values within the range of a type  everything works   When you approach the lower or upper bound of a type  you encounter a discontinuity  and you can get unexpected results  For signed integer types  the problems occur only for very large negative and positive values  exceeding INT MIN and INT MAX  For unsigned integer types  problems occur for very large positive values and at zero  This can be a source of bugs  For example  this is an infinite loop   for  unsigned int i   10  i  gt   0  i --        printf   u n   i       because i is always greater than or equal to zero  that s the nature of unsigned types   Inside the loop  when i is zero  i-- sets its value to UINT MAX

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In practice  there are two differences   printing  eg with cout in C   or printf in C   unsigned integer bit representation is interpreted as a nonnegative integer by print functions  ordering  the ordering depends on signed or unsigned specifications   this code can identify the integer using ordering criterion  char a   0  a--  if  0  lt  a      printf  quot unsigned quot    else     printf  quot signed quot     char is considered signed in some compilers and unsigned in other compilers  The code above determines which one is considered in a compiler  using the ordering criterion  If a is unsigned  after a--  it will be greater than 0  but if it is signed it will be less than zero  But in both cases  the bit representation of a is the same  That is  in both cases a-- does the same change to the bit representation

[c] What is the difference between signed and unsigned int

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