Serial problems... ÿ

I need help guys...
As I use my arduino serial with this program:

int ledArduino=13;

void setup()

void loop()
if(Serial.available() > 0){

if ('0'){ //LED ON
if ('1'){ //LED OFF


And as I use it by my pc serial monitor, it doesn't work, and when it works it returns me this symbol: ÿ
Apart of this, sometimes, it works but not in the correct way... it only works with the first "IF()" inside the IF(Serial.available()>0){,the rest of the code didnt work... so in this case, i just could open the pin 13 led.

If the first character you read isn't a '0', read another character . . . that hasn't arrived yet.
No. Bad idea.

Read once, compare many.

Very simple LED on/off serial code.

// zoomkat 8-6-10 serial I/O string test
// type a string in serial monitor. then send or enter
// for IDE 0019 and later

//A very simple example of sending a string of characters 
//from the serial monitor, capturing the individual 
//characters into a String, then evaluating the contents 
//of the String to possibly perform an action (on/off board LED).

int ledPin = 13;
String readString;

void setup() {
  pinMode(ledPin, OUTPUT); 
  Serial.println("serial on/off test 0021"); // so I can keep track

void loop() {

  while (Serial.available()) {
    char c =;
    readString += c; 

  if (readString.length() >0) {

    if(readString.indexOf("on") >=0)
      digitalWrite(ledPin, HIGH);

    if(readString.indexOf("off") >=0)
      digitalWrite(ledPin, LOW);