How to convert a single char into an int

Question

I have a string of digits  e g   123456789   and I need to extract each one of them to use them in a calculation  I can of course access each char by index  but how do I convert it into an int   I ve looked into atoi    but it takes a string as argument  Hence I must convert each char into a string and then call atoi on it  Is there a better way

User · Answer

The answers provided are great as long as you only want to handle Arabic numerals, and are working in an encoding where those numerals are sequential, and in the same place as ASCII.

This is almost always the case.

If it isn't then you need a proper library to help you.

Let's start with ICU.

First convert the byte-string to a unicode string. (Left as an exercise for the reader).
Then use uchar.h to look at each character.
if we the character is UBool u_isdigit (UChar32 c)
then the value is int32_t u_charDigitValue ( UChar32 c )

Or maybe ICU has some function to do it for you - I haven't looked at it in detail.

User · Answer

The answers provided are great as long as you only want to handle Arabic numerals, and are working in an encoding where those numerals are sequential, and in the same place as ASCII.

This is almost always the case.

If it isn't then you need a proper library to help you.

Let's start with ICU.

First convert the byte-string to a unicode string. (Left as an exercise for the reader).
Then use uchar.h to look at each character.
if we the character is UBool u_isdigit (UChar32 c)
then the value is int32_t u_charDigitValue ( UChar32 c )

Or maybe ICU has some function to do it for you - I haven't looked at it in detail.

User · Answer

Any problems with the following way of doing it   int CharToInt const char c        switch  c            case  0           return 0      case  1           return 1      case  2           return 2      case  3           return 3      case  4           return 4      case  5           return 5      case  6           return 6      case  7           return 7      case  8           return 8      case  9           return 9      default          return 0

User · Answer

Any problems with the following way of doing it   int CharToInt const char c        switch  c            case  0           return 0      case  1           return 1      case  2           return 2      case  3           return 3      case  4           return 4      case  5           return 5      case  6           return 6      case  7           return 7      case  8           return 8      case  9           return 9      default          return 0

User · Answer

define toDigit c   c- 0

User · Answer

By this way You can convert char to int and int to char easily   int charToInt char c       int arr    0 1 2 3 4 5 6 7 8 9      return arr c- 0

User · Answer

You can make use of atoi   function   include  lt stdlib h gt   include  lt stdio h gt  int main int argc  char  argv         int num       num   atoi argv 1        printf   n d   num

User · Answer

For me the following worked quite well   QChar c    5   int x   c digitValue       x is now 5   Documentation  int QChar  digitValue   const which says      Returns the numeric value of the digit  or -1 if the character is not   a digit

User · Answer

You can utilize the fact that the character encodings for digits are all in order from 48  for  0   to 57  for  9    This holds true for ASCII  UTF-x and practically all other encodings  see comments below for more on this    Therefore the integer value for any digit is the digit minus  0   or 48    char c    1   int i   c -  0      i is now equal to 1  not  1    is synonymous to  char c    1   int i   c - 48     i is now equal to 1  not  1    However I find the first c -  0  far more readable

User · Answer

By this way You can convert char to int and int to char easily   int charToInt char c       int arr    0 1 2 3 4 5 6 7 8 9      return arr c- 0

User · Answer

If you are worried about encoding  you can always use a switch statement     Just be careful with the format you keep those large numbers in   The maximum size for an integer in some systems is as low as 65 535  32 767 signed    Other systems  you ve got 2 147 483 647  or 4 294 967 295 unsigned

User · Answer

You can utilize the fact that the character encodings for digits are all in order from 48  for  0   to 57  for  9    This holds true for ASCII  UTF-x and practically all other encodings  see comments below for more on this    Therefore the integer value for any digit is the digit minus  0   or 48    char c    1   int i   c -  0      i is now equal to 1  not  1    is synonymous to  char c    1   int i   c - 48     i is now equal to 1  not  1    However I find the first c -  0  far more readable

User · Answer

If you are worried about encoding  you can always use a switch statement     Just be careful with the format you keep those large numbers in   The maximum size for an integer in some systems is as low as 65 535  32 767 signed    Other systems  you ve got 2 147 483 647  or 4 294 967 295 unsigned

User · Answer

Any problems with the following way of doing it   int CharToInt const char c        switch  c            case  0           return 0      case  1           return 1      case  2           return 2      case  3           return 3      case  4           return 4      case  5           return 5      case  6           return 6      case  7           return 7      case  8           return 8      case  9           return 9      default          return 0

User · Answer

Or you could use the  correct  method  similar to your original atoi approach  but with std  stringstream instead  That should work with chars as input as well as strings   boost  lexical cast is another option for a more convenient syntax    atoi is an old C function  and it s generally recommended to use the more flexible and typesafe C   equivalents where possible  std  stringstream covers conversion to and from strings

User · Answer

define toDigit c   c- 0

User · Answer

Or you could use the  correct  method  similar to your original atoi approach  but with std  stringstream instead  That should work with chars as input as well as strings   boost  lexical cast is another option for a more convenient syntax    atoi is an old C function  and it s generally recommended to use the more flexible and typesafe C   equivalents where possible  std  stringstream covers conversion to and from strings

User · Answer

Or you could use the  correct  method  similar to your original atoi approach  but with std  stringstream instead  That should work with chars as input as well as strings   boost  lexical cast is another option for a more convenient syntax    atoi is an old C function  and it s generally recommended to use the more flexible and typesafe C   equivalents where possible  std  stringstream covers conversion to and from strings

User · Answer

You can make use of atoi   function   include  lt stdlib h gt   include  lt stdio h gt  int main int argc  char  argv         int num       num   atoi argv 1        printf   n d   num

User · Answer

If you are worried about encoding  you can always use a switch statement     Just be careful with the format you keep those large numbers in   The maximum size for an integer in some systems is as low as 65 535  32 767 signed    Other systems  you ve got 2 147 483 647  or 4 294 967 295 unsigned

User · Answer

Or you could use the  correct  method  similar to your original atoi approach  but with std  stringstream instead  That should work with chars as input as well as strings   boost  lexical cast is another option for a more convenient syntax    atoi is an old C function  and it s generally recommended to use the more flexible and typesafe C   equivalents where possible  std  stringstream covers conversion to and from strings

User · Answer

include lt iostream gt   include lt stdlib gt  using namespace std   void main          char ch       int x       cin  gt  gt  ch       x   char  ar 1         cout  lt  lt  x

User · Answer

include lt iostream gt   include lt stdlib gt  using namespace std   void main          char ch       int x       cin  gt  gt  ch       x   char  ar 1         cout  lt  lt  x

User · Answer

include lt iostream gt   include lt stdlib gt  using namespace std   void main          char ch       int x       cin  gt  gt  ch       x   char  ar 1         cout  lt  lt  x

User · Answer

If you are worried about encoding  you can always use a switch statement     Just be careful with the format you keep those large numbers in   The maximum size for an integer in some systems is as low as 65 535  32 767 signed    Other systems  you ve got 2 147 483 647  or 4 294 967 295 unsigned

User · Answer

You can utilize the fact that the character encodings for digits are all in order from 48  for  0   to 57  for  9    This holds true for ASCII  UTF-x and practically all other encodings  see comments below for more on this    Therefore the integer value for any digit is the digit minus  0   or 48    char c    1   int i   c -  0      i is now equal to 1  not  1    is synonymous to  char c    1   int i   c - 48     i is now equal to 1  not  1    However I find the first c -  0  far more readable

User · Answer

For me the following worked quite well   QChar c    5   int x   c digitValue       x is now 5   Documentation  int QChar  digitValue   const which says      Returns the numeric value of the digit  or -1 if the character is not   a digit

User · Answer

Any problems with the following way of doing it   int CharToInt const char c        switch  c            case  0           return 0      case  1           return 1      case  2           return 2      case  3           return 3      case  4           return 4      case  5           return 5      case  6           return 6      case  7           return 7      case  8           return 8      case  9           return 9      default          return 0

User · Answer

You can utilize the fact that the character encodings for digits are all in order from 48  for  0   to 57  for  9    This holds true for ASCII  UTF-x and practically all other encodings  see comments below for more on this    Therefore the integer value for any digit is the digit minus  0   or 48    char c    1   int i   c -  0      i is now equal to 1  not  1    is synonymous to  char c    1   int i   c - 48     i is now equal to 1  not  1    However I find the first c -  0  far more readable

User · Answer

include lt iostream gt   include lt stdlib gt  using namespace std   void main          char ch       int x       cin  gt  gt  ch       x   char  ar 1         cout  lt  lt  x

[c++] How to convert a single char into an int

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