Determine if char is a num or letter

Question

How do I determine if a char in C such as a or 9 is a number or a letter   Is it better to use   int a   Asc theChar     or this   int a    int theChar

User · Answer

You can normally check for ASCII letters or numbers using simple conditions

if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
{
    /*This is an alphabet*/
}

For digits you can use

if (ch >= '0' && ch <= '9')
{
    /*It is a digit*/
}

But since characters in C are internally treated as ASCII values you can also use ASCII values to check the same.

How to check if a character is number or letter

User · Answer

If  theChar  gt    0   amp  amp  theChar  lt   9   it s a digit  You get the idea

User · Answer

lt ctype h gt  includes a range of functions for determining if a char represents a letter or a number  such as isalpha  isdigit and isalnum   The reason why int a    int theChar won t do what you want is because a will simply hold the integer value that represents a specific character  For example the ASCII number for  9  is 57  and for  a  it s 97   Also for ASCII    Numeric - if  theChar  gt    0   amp  amp  theChar  lt    9   Alphabetic -  if  theChar  gt    A   amp  amp  theChar  lt    Z     theChar  gt    a   amp  amp  theChar  lt    z     Take a look at an ASCII table to see for yourself

User · Answer

chars are just integers  so you can actually do a straight comparison of your character against literals   if  c  gt    0   amp  amp  c  lt    9       This applies to all characters   See your ascii table   ctype h also provides functions to do this for you

User · Answer

Neither of these does anything useful  Use isalpha   or isdigit   from the standard library  They re in  lt ctype h gt

User · Answer

You ll want to use the isalpha   and isdigit   standard functions in  lt ctype h gt    char c    a      or whatever  if  isalpha c         puts  it s a letter      else if  isdigit c         puts  it s a digit      else       puts  something else

User · Answer

C99 standard on c  gt    0   amp  amp  c  lt    9   c  gt    0   amp  amp  c  lt    9   mentioned in another answer  works because C99 N1256 standard draft 5 2 1  Character sets  says      In both the source and execution basic character sets  the   value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous    ASCII is not guaranteed however

[c] Determine if char is a num or letter

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