/* converts a string of hexadecimal digits (including an optional 0x
 * or 0X) into its equivalent integer value. The allowable digits are
 * 0 through 9, a through f, and A through F.
 */

#define MAXLEN 50 /* maximum allowable length of the number to be converted */

#include <stdio.h>
#include <ctype.h>

int main() {
     char c, count, arg[MAXLEN];
     int result;
     
     count = 0;
     while ((c = getchar()) != EOF && c != '\t' && c != '\n' && c != ' ') {
	  if (count < MAXLEN)
	       arg[count++] = c;
	  else
	       break;
     }
     
     arg[count] = '\0';
     result = htoi(arg);
     printf("Hex entered: %s\n", arg);
     printf("Integer equivalent: %d\n", result);
     return 0;
}

int htoi(char arg[]) {
     int i, result;

     i = result = 0;

     if (arg[i] == '0') {
	  i++;
	  if (arg[i] == 'x' || arg[i] == 'X')
	       i++;
     }

     while (arg[i] != '\0') {
	  if (arg[i] >= 'a' && arg[i] <= 'f') {
	       result = result * 16 + arg[i] - 'a' + 10;
	       i++;
	  } else if (arg[i] >= 'A' && arg[i] <= 'F') {
	       result = result * 16 + arg[i] - 'A' + 10;
	       i++;
	  } else if (arg[i] >= '0' && arg[i] <= '9') {
	       result = result * 16 + arg[i] - '0';
	       i++;
	  } else {
	       printf("Invalid data, foo.\n");
	       exit(0);
	  }
     }

     return result;
}

/* i'm a noob */