Isalpha and isalnum

When I write a C-language identifier for a few days, I see someone else'sCodeThere are isalpha and isalnum, which saves a lot of trouble compared to my code. Baidu only knows that there are already ready-made functions available.

Both functions are included in # include <ctype. h>, where int isalpha (INT ch) is used to determine whether ch is a English letter, when it is an English letter A-Z or A-Z, in standard C is equivalent to using isupper (CH) (determine whether ch is a capital letter) | islower (CH) (determine whether ch is a lowercase letter) returns a non-zero value; otherwise, return zero;

Int isalnum (int c) is similar to int isalpha, but it has a wider scope of judgment and can also determine 0-9 numbers, that is, when it is an English letter A-Z or A-Z or 0-9, it returns a non-zero value, otherwise it returns zero;