K&R2 Exercise 2-3

2-3.c

/*K&R2 Exercise 2-3 "htoi"*/
#include <stdio.h>
#include <ctype.h>

int htoi(char[]);
int getl(char[], int);

int main()
{
	char s[20];
	int c;
	while((c = getl(s, 20)))
		printf("%d\n", htoi(s));
}

int getl(char s[], int lim)
{
	int c, i;

	for(i = 0; i < lim-1 && (c = getchar()) != EOF && c !='\n'; ++i)
		s[i] = c;
	if(c == '\n') {
		s[i] = c;
		++i;
	}
	s[i] = '\0';
	return i;
}

int htoi(char s[])
{
	int i, n;
	n = 0;
	for(i = 0; s[i] != '\0'; i++)
		s[i] = tolower(s[i]);
	for(i = 0; s[i] != '\0'; i++)
		if(isdigit(s[i]))
			n = 16 * n + (s[i] - '0');
		else if(s[i] >= 'a' && s[i] <= 'f')
			n = 16 * n + (s[i] - 87);
		else if(s[i] != 'x' || s[i] != '\n')
			return -1;
	return n;
}