Reading text/strings via processing

Question

I'm trying to control an led attached to my arduino via key presses on my laptop.When i hold down a key, the led should light up, and when i release the key, the led should turn off.

While my code works ATM, i am wondering why my code will not work if i replace the numbers in my code with text/strings.

Processing code(Working)

import processing.serial.*;
Serial myPort;

void setup(){
  println("The available ports are: ");
  println(Serial.list());
  myPort = new Serial(this,Serial.list()[0],9600);
  myPort.buffer(8);
  size(500, 500);
}

void draw(){
  if(keyPressed){
    if(key == 'r' || key == 'R'){
      myPort.write(1);
      println("red");
    }

  }

}

void keyReleased(){
  myPort.write(2);println("released");
}

Arduino Code(Working)

int red = 7;

void setup(){
  Serial.begin(9600);
  pinMode(red,OUTPUT);
}

void loop(){

}

void serialEvent(){
    int input = Serial.read();
  if(input == 1){
    digitalWrite(red,HIGH);
  }else if(input == 2){
    digitalWrite(red,LOW);
  }
}

Processing Code (Not working)

import processing.serial.*;
Serial myPort;

void setup(){
  println("The available ports are: ");
  println(Serial.list());
  myPort = new Serial(this,Serial.list()[0],9600);
  myPort.buffer(8);
  size(500, 500);
}

void draw(){
  if(keyPressed){
    if(key == 'r' || key == 'R'){
      myPort.write("red");
      println("red");
    }

  }

}

void keyReleased(){
  myPort.write("released");
  println("released");
}

Arduino Code(Not working)

int red = 7;

void setup(){
  Serial.begin(9600);
  pinMode(red,OUTPUT);
}

void loop(){

}

void serialEvent(){
    int input = Serial.read();
  if(input == "red"){
    digitalWrite(red,HIGH);
  }else if(input == "released"){
    digitalWrite(red,LOW);
  }
}

From the above example, i get the error ISO C++ forbids comparisons between pointers and integers.After googling the error, it was suggested that i replace the double quotes with single quotes, after which the arduino code is able to compile, but the processing code gives an error "badly formed character constant(expecting quote,got e)".

I then tried changing using double quotes for processing and single quotes for the arduino quote, but predictably, it did not work.

Why does my code work when i pass numbers to the arduino via serial communication, and my code fails when i use text strings?

Answer 1

The problem is that you're mixing different variable types. It's kinda an oil/water scenario.

Basically, the serial.read(); command returns an integer, -1 if there's nothing in the buffer. If there is something, it will return the character code (i.e. 93 = a). Because of that, it's an integer. When you put something in single quotes, it compiles as the equivalent ISO character code.

So, when you do input == 2, it is integer [compared to] integer. When you do input == "string", you're doing integer [compared to] string, thus you get errors. BTW: a string is a type of pointer.

So, what you have to do is this:

string input = "";
if(serial.avaliable()) {
    delay(100); //Wait for all data to be received
    while(serial.avaliable()) {
        string = string + char(serial.read());
    }
}
if(input == "yay_it_works!) {
    //Done!
}