Convert char to int in C and C

Question

How do I convert a char to an int in C and C

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Well  in ASCII code  the numbers  digits  start from 48  All you need to do is  int x    int character - 48   Or  since the character  0  has the ASCII code of 48  you can just write  int x   character -  0       The  int  cast is not necessary

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C and C   always promote types to at least int  Furthermore character literals are of type int in C and char in C     You can convert a char type simply by assigning to an int    char c    a      narrowing on C int a   c

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It sort of depends on what you mean by  convert     If you have a series of characters that represents an integer  like  123456   then there are two typical ways to do that in C  Use a special-purpose conversion like atoi   or strtol    or the general-purpose sscanf    C    which is really a different language masquerading as an upgrade  adds a third  stringstreams   If you mean you want the exact bit pattern in one of your int variables to be treated as a char  that s easier  In C the different integer types are really more of a state of mind than actual separate  types   Just start using it where chars are asked for  and you should be OK  You might need an explicit conversion to make the compiler quit whining on occasion  but all that should do is drop any extra bits past 256

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For char or short to int  you just need to assign the value   char ch   16  int in   ch    Same to int64   long long lo   ch    All values will be 16

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char is just a 1 byte integer  There is nothing magic with the char type  Just as you can assign a short to an int  or an int to a long  you can assign a char to an int   Yes  the name of the primitive data type happens to be  char   which insinuates that it should only contain characters  But in reality   char  is just a poor name choise to confuse everyone who tries to learn the language  A better name for it is int8 t  and you can use that name instead  if your compiler follows the latest C standard   Though of course you should use the char type when doing string handling  because the index of the classic ASCII table fits in 1 byte  You could however do string handling with regular ints as well  although there is no practical reason in the real world why you would ever want to do that  For example  the following code will work perfectly     int str       h    e    l    l    o     0        for i 0  i lt 6  i            printf   c   str i          You have to realize that characters and strings are just numbers  like everything else in the computer  When you write  a  in the source code  it is pre-processed into the number 97  which is an integer constant   So if you write an expression like  char ch    5   ch   ch -  0     this is actually equivalent to  char ch    int 53  ch   ch -  int 48    which is then going through the C language integer promotions  ch    int ch -  int 48    and then truncated to a char to fit the result type  ch    char    int ch -  int 48      There s a lot of subtle things like this going on between the lines  where char is implicitly treated as an int

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Presumably you want this conversion for using functions from the C standard library   In that case  do  C   syntax   typedef unsigned char UChar   char myCppFunc  char c         return char  someCFunc  UChar  c            The expression UChar  c   converts to unsigned char in order to get rid of negative values  which  except for EOF  are not supported by the C functions   Then the result of that expression is used as actual argument for an int formal argument  Where you get automatic promotion to int  You can alternatively write that last step explicitly  like int  UChar  c      but personally I find that too verbose   Cheers  amp  hth

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int charToint char a   char  p    amp a  int k   atoi p   return k      You can use this atoi method for converting char to int  For more information  you can refer to this http   www cplusplus com reference cstdlib atoi    http   www cplusplus com reference string stoi

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I have absolutely null skills in C  but for a simple parsing        char  something    123456    int number   parseInt something        this worked for me   int parseInt char  chars        int sum   0      int len   strlen chars       for  int x   0  x  lt  len  x                  int n   chars len -  x   1   -  0           sum   sum   powInt n  x             return sum     int powInt int x  int y        for  int i   0  i  lt  y  i                  x    10            return x

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I was having problems converting a char array like  7c7c7d7d7d7d7c7c7c7d7d7d7d7c7c7c7c7c7c7d7d7c7c7c7c7d7c7d7d7d7c7c2e2e2e  into its actual integer value that would be able to be represented by  7C  as one hexadecimal value  So  after cruising for help I created this  and thought it would be cool to share   This separates the char string into its right integers  and may be helpful to more people than just me     unsigned int  char2int char  a  int len        int i u      unsigned int  val   malloc len sizeof unsigned long         for i 0 u 0 i lt len i             if i 2  0               if a i   lt   57                  val u     a i -50  lt  lt 4              else                 val u     a i -55  lt  lt 4                    else              if a i   lt   57                  val u      a i -50               else                 val u      a i -55               u                        return val      Hope it helps

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This answer addresses the C   side of things  but the sign extension problem exists in C too    Handling all three char types  signed  unsigned  and char  is more delicate than it first appears  Values in the range 0 to SCHAR MAX  which is 127 for an 8-bit char  are easy   char c   somevalue  signed char sc   c  unsigned char uc   c  int n   c    But  when somevalue is outside of that range  only going through unsigned char gives you consistent results for the  same  char values in all three types   char c   somevalue  signed char sc   c  unsigned char uc   c     Might not be true  int c     int sc  and int c     int uc   int nc    unsigned char c  int nsc    unsigned char sc  int nuc    unsigned char uc     Always true  nc    nsc and nc    nuc    This is important when using functions from ctype h  such as isupper or toupper  because of sign extension   char c   negative char      Assuming CHAR MIN  lt  0  int n   c  bool b   isupper n       Undefined behavior    Note the conversion through int is implicit  this has the same UB   char c   negative char  bool b   isupper c     To fix this  go through unsigned char  which is easily done by wrapping ctype h functions through safe ctype   template lt int   amp F  int  gt  int safe ctype unsigned char c    return F c            char c   CHAR MIN  bool b   safe ctype lt isupper gt  c       No UB   std  string s    value that may contain negative chars  e g  user input   std  transform s begin    s end    s begin     amp safe ctype lt toupper gt       Must wrap toupper to eliminate UB in this case  you can t cast    to unsigned char because the function is called inside transform    This works because any function taking any of the three char types can also take the other two char types   It leads to two functions which can handle any of the types   int ord char c    return  unsigned char c    char chr int n      assert 0  lt   n       Or other error- sanity-checking    assert n  lt   UCHAR MAX     return  unsigned char n        Ord and chr are named to match similar functions in other languages    and libraries    ord c  always gives you a non-negative value     even when passed a negative char or negative signed char     and chr takes any value ord produces and gives back the exact same char   In practice  I would probably just cast through unsigned char instead of using these  but they do succinctly wrap the cast  provide a convenient place to add error checking for int-to-char  and would be shorter and more clear when you need to use them several times in close proximity

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Depends on what you want to do   to read the value as an ascii code  you can write  char a    a   int ia    int a      note that the int cast is not necessary -- int ia   a would suffice      to convert the character  0  - gt  0   1  - gt  1  etc  you can write  char a    4   int ia   a -  0      check here if ia is bounded by 0 and 9      Explanation  a -  0  is equivalent to   int a  -   int  0    which means the ascii values of the characters are subtracted from each other  Since 0 comes directly before 1 in the ascii table  and so on until 9   the difference between the two gives the number that the character a represents

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Use static cast lt int gt    int num   static cast lt int gt  letter      if letter  a   num 97     Edit  You probably should try to avoid to use  int      int num    int  letter    check out Why use static cast lt int gt  x  instead of  int x  for more info

[c++] Convert char to int in C and C++

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