convert ascii to integer without using atoi()

int _asc2int(const char* s)
{
	int i = 0; 
	// return 0 on any other character
	while (*s != 0)
	{
		if (*s >= '0' && *s <= '9')
		{
			i = i * 10 + (*s - '0');
			s++;
		}
		else return 0; 
	}
	return i;
 
}
int asc2int(const char* s)
{
	// leading '+' and '-' allowed
	int sign = 1; 
	if (*s == '+') s++;
	if (*s == '-')
	{
		sign = -1;
		s++;
	}
	return _asc2int(s) * sign;
}
 
int main()
{
	char s[] = "-975310";
	printf("'%s' => %dn", s, asc2int(s));
        return 0;
}