Newbie question about error: invalid conversion

Forum 2005-2010 (read only) Software Troubleshooting
1

Hey all,

Two days ago I started playing around with arduino, so I am completely new to the programming of the arduino board. also I don't know processing. (I do fine with webbased programming though, like actionscript & php)

However, I did get the blinking led sketch to work, and amended it to say "hello world" in morse, controlling a Relaysboard and a 230v lightbulb. All very exciting for my taste, however I need it to do a lot more: my Arduino's planned to become the beating hardware heart of my graduation installation.

So, now I run into a problem. My following code is accepted by Arduino 0003, by rejected by 0004. It says:

In function 'void loop()':
error: invalid conversion from 'const char*' to 'unsigned char

This is the code I have. Can anybody tell me what I am doing wrong?

int joyPin = 2;
int joyVal = 0;

void setup()
{
  beginSerial(9600);
  pinMode(joyPin, INPUT);   
}
void loop()
{
  joyVal = digitalRead(joyPin);
  if (joyVal == HIGH){
    serialWrite("A");
  }   
  else{
    serialWrite("B");
  }
  delay(100);
}
2

Gosh, changing "serialWrite("blabla");" to "Serial.print("blabla");" has a magical effect on this problem.

Excuse me for my noobness :wink:

3

Don't worry, it's actually a subtle issue. In C and C++, "A" is a string, i.e. a pointer to sequence of characters. A single character is written with single quotes, e.g. 'A'. In C, functions cannot be overloaded, i.e. you can't have a version of serialWrite for strings and another for characters. C will, however, happily convert a string like "A" to a character (which is what serialWrite is designed for) - but it won't do so in the way you expect. That is, "A" gets converted into the character whose ASCII code equals the address of the string. In C++, you can overload functions, so there's a version of Serial.print() for both characters and strings (and integers, etc) that does what you'd expect.