Reading Serial Port in arduino

Reading a number in arduino from a connected device through serial

char serString[4]; // 4 padded string ie 1111
int ledPin = 9; // to test input on an LED
int serInt;  //integer that comes out
void setup()
{
  Serial.begin(9600);	
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  readSerial(serString); //read the serial port
  serInt = atoi(serString);
if serInt is more than 0 then do whatever is in the if statement 
  if (serInt > 0){
    Serial.println(serInt);
    analogWrite(ledPin, serInt);
    clearSerial();
  }
 delay(50);
}
//function to read serial 
void readSerial(char *strArray) {
  int i = 0;
    if(!Serial.available()) {
       return;
      }
//if serial has something read each figure and put it in char array
    while (Serial.available()) { 
          strArray[i] = Serial.read();
          i++;
      }  
}
//clear the char array of any previous data
void clearSerial() {
    for (int i=0; i < 4; i++) {
      serString[i] = ' ';
    }

Processing Code to listen to one sensor with serialEvent()

/**
Code for reading in data from one sensor on an arduino
Pete Rogers 19/12/2008 17:20
**/

import processing.serial.*;

int lf = 10;                  // Linefeed in ASCII
int myWidth = 1024;           // stage width
int myHeight = 1024;          //stage height
String sensorString = null;   //string  holding raw data from arduino
int sensorInt = 0;            //number from sensor
Serial myPort;                // The serial port 

void setup() {
  size(myWidth, myHeight);    //set up the stage window   
  frameRate(30);              //set frame rate playback
  smooth();                   //make the visual quality high 
//lines below open and configure the serial port
  println(Serial.list()); 
  myPort = new Serial(this, Serial.list()[1], 9600); 
  myPort.clear();            
  sensorString = myPort.readStringUntil(lf); 
  sensorString = null;                       
}

void draw() {
      background(0); //repaints background
      ellipse(myWidth/2,myHeight/2, sensorInt, sensorInt); //draws circle
}

//serialEvent function is triggered whenever there is data from the arduino
void serialEvent(Serial myPort){
       sensorString = myPort.readStringUntil(lf);
      if ( sensorString != null) {
             sensorString = trim( sensorString);
            sensorInt = int( sensorString);
    }
}