c - Change letter with number -

i'm doing exercise, practice, point receive string of numbers , letters, check if it's letter, transforme number rule

a = 10, z = 35 

and place in array. operations after.

i know how except rule part, no idea how check letter , how replace right number. know there's way like

     if(string[x] == 'a-z') 

but i'm neither sure how works, or how pick right number knowing it's letter.

there many approaches, more portable others.

the following looks thestring[x] in array. if successful, pointer difference between , start value.

const char *alphanum = "0123456789abcdefghijklmnopqrstuvwxyz"; char *p = strchr(alphanum, string[x]); if (p == null || *p == '\0') {   ; // not digit or a-z } else {   int value = p - alphanum;   // value;       } 

i'll leave handling of a-z op. (convert upper or use array)

if code assumes ascii, a z in sequential order:

int tovalue(char ch) {   if (ch >= 'a' && ch <= 'z') return ch - 'a' + 10;   if (ch >= 'a' && ch <= 'z') return ch - 'a' + 10;   if (ch >= '0' && ch <= '9') return ch - '0';   // no match   return -1; }