int index, last;

char int2char(int n) {
  return (n > 9) ? ' ' : n+'0';
}

int char2int(char c) {
  return (isdigit(c)) ? int(c-'0') : -1;
}


void setup() {
  Serial.begin(9600);
  
  for (int i=33; i<64; i++)
    Serial.print(i),
    Serial.print(": "),
    Serial.println((char)i);

  last = -1;
  index = 0;
}

void loop(){
  if (Serial.available() > 0) {
    char c = Serial.read();

    if (isprint(c)) {
      int val = char2int(c);
      last = val;
    }


  }
}