Multiple Serial Programme Error!

Hi everyone, I really need your help. Okay here's what I'm trying to do from what I know Arduino Mega have 3 additional serial port , so in total there's 4. It's just nice since I got 4 in my hand right now which I want it to work with Arduino Mega. However, after I do up a simple coding from scratch and verifying it there's error so here's my coding :

//Testing with one more serial devices that shall be written in the comment status
#include <SoftwareSerial.h>

/*
This file is to integrate : pH , tds , blow off and fill  in sensor into Arduino Mega 
 */
//TDS
#define rxpin  2                                                                //set the RX pin to pin 2
#define txpin  3                                                                //set the TX pin to pin 3
//pH
#define rxpin1 19
#define txpin1 18
//Blow OFF
#define rxpin2 17
#define txpin2 16
//FILL IN
#define rxpin3 15
#define txpin3 14

//ColorDetector Sensor
//#define rxpin4 4
//#define txpin4 5

SoftwareSerial myserial(rxpin,txpin);
//SoftwareSerial myserial4(rxpin4, txpin4);                                         //enable the soft serial port


String inputstring = "";                                                       //a string to hold incoming data from the PC
String sensorstring = "";                                                      //a string to hold the data from the Atlas Scientific product
boolean input_stringcomplete = false;                                          //have we received all the data from the PC
boolean sensor_stringcomplete = false;                                         //have we received all the data from the Atlas Scientific product


void setup(){                                                                //set up the hardware
  Serial.begin(38400);                                                      //set baud rate for the hardware serial port to 38400
  //Serial for TDS emulated virtual port
  myserial.begin(38400);                                                    //set baud rate for software serial port to 38400
  //rx and tx for pH pin 19 & 18
  Serial1.begin(38400);
  //rx and tx for BLOW OFF pin 17 & 16  
  Serial2.begin(38400);
  //rx and tx for Fill IN pin 15 & 14
  Serial3.begin(38400);
  inputstring.reserve(5);                                                   //set aside some bytes for receiving data from the PC
  sensorstring.reserve(30);                                                 //set aside some bytes for receiving data from Atlas Scientific product
}



void serialEvent() {                                                         //if the hardware serial port receives a char
  char inchar = (char)Serial.read();                               //get the char we just received
  inputstring += inchar;                                           //add it to the inputString
  if(inchar == '\r') {
    input_stringcomplete = true;
  }                //if the incoming character is a <CR>, set the flag
}  



void loop(){                                                                   //here we go....

  if (input_stringcomplete){                                                   //if a string from the PC has been recived in its entierty 
    myserial.print(inputstring);                                             //send that string to the Atlas Scientific product
    inputstring = "";                                                        //clear the string:
    input_stringcomplete = false;                                            //reset the flage used to tell if we have recived a completed string from the PC
  }
//FILL IN 
  while(Serial3.available()){
    char inchar = (char)myserial.read();                                  //get the new char
    sensorstring += inchar;                                               //add it to the sensorString
    if (inchar == '\r') {
      sensor_stringcomplete = true;
    }
  }
//BLOW OFF 
  while(Serial2.available()){
    char inchar = (char)myserial.read();                                  //get the new char
    sensorstring += inchar;                                               //add it to the sensorString
    if (inchar == '\r') {
      sensor_stringcomplete = true;
    }
  }
//pH 
  while(Serial1.available()){
    char inchar = (char)myserial.read();                                  //get the new char
    sensorstring += inchar;                                               //add it to the sensorString
    if (inchar == '\r') {
      sensor_stringcomplete = true;
    }
   }
//TDS
  while (myserial.available()) {                                               //while a char is holding in the serial buffer
    char inchar = (char)myserial.read();                                  //get the new char
    sensorstring += inchar;                                               //add it to the sensorString
    if (inchar == '\r') {
      sensor_stringcomplete = true;
    }                   //if the incoming character is a <CR>, set the flag
  }


  if (sensor_stringcomplete){                                                 //if a string from the Atlas Scientific product has been received in its entirety
    Serial.print(sensorstring);                                             //use the hardware serial port to send that data to the PC
    sensorstring = "";                                                      //clear the string:
    sensor_stringcomplete = false;                                          //reset the flag used to tell if we have received a completed string from the Atlas Scientific product
  }
}

I solved the problem through researching the threads here
http://forum.arduino.cc/index.php/topic,93007.0.html

Anyway one more problem is that if I write something on my Serial monitor based on my coding would it send it to the rest of the serial devices together at the same time?

Thanks everyone...

I don't have time to follow your link just now.

You don't use Software Serial for the hardware serial ports on the Mega. Just Serial1.begin() Serial2.begin() etc.

The Serial Monitor only communicates with its own Serial connection and has nothing to do with the other 3.

...R

Thanks Robin2 for replying. I understand and will make amendments. Thanks again.