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Author Topic: [SOLVED] switch case with strings  (Read 12490 times)
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I'm trying to control a single RGB LED using a switch case, but I keep getting this error:
Code:
error: case label does not reduce to an integer constant

My code looks like this:
Code:
void ledColor(char color) {
  switch (color) {
    case "clear":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 0);
      break;
    case "red":
      digitalWrite(redPin, 255);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 0);
      break;
    case "green":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 255);
      digitalWrite(bluePin, 0);
      break;
    case "blue":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 255);
      break;
  }
}

and it is called like this:
Code:
ledColor("blue");

I'm pretty new at this. I tried the "char" type because "string" doesn't seem to be present in the Arduino syntax.

What am I missing or doing wrong?
« Last Edit: December 22, 2010, 11:17:33 am by mrbug » Logged

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The message pretty much tells you what the problem is.
Quote
"error: case label does not reduce to an integer constant"

http://gd.tuwien.ac.at/languages/c/programming-bbrown/c_028.htm
Quote
Rules for switch statements

      [glow]values for 'case' must be integer or character constants[/glow]
      the order of the 'case' statements is unimportant
      the default clause may occur first (convention places it last)
      you cannot use expressions or ranges

Your are not. Strings (null terminated arrays of characters) are not characters.

You can not use a switch statement in the way you are trying to.

This is also a problem:
Code:
void ledColor(char color) {

Code:
ledColor("blue");
"blue" is not a character. It is an array of characters.
« Last Edit: December 22, 2010, 09:16:58 am by PaulS » Logged

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Quote
"blue" is not a character. It is an array of characters.

Yeah, that's why I was wondering what I could do to make the strings work. Should I just change it to r/g/b/c instead or is there something else entirely that I should do?

EDIT:

Okay, I changed it to just r/g/b/c. However, I'm still getting
Code:
error: case label does not reduce to an integer constant
and
Code:
error: invalid conversion from 'const char*' to 'char'
error: initializing argument 1 of 'void ledColor(char)'

EDIT 2:
If I put "char color = 'c';" in the variable section of my code, it doesn't complain as much. However, I still get this error:
Code:
error: variable or field 'ledColor' declared void
error: 'color' was not declared in this scope
error: invalid conversion from 'const char*' to 'char'

Is color a reserved word that I don't know about?
« Last Edit: December 22, 2010, 09:58:20 am by mrbug » Logged

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Psst, we can't see your code.
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Ah, good point. Here you go:

Code:
// physical mailbox checker (PMC)
// ------------------------
// 1. photoresistor detects "box open" state. blue activity LED is enabled.
// 2. if pressure sensor detects mail, green "mail present" LED is enabled.
// 3. if pressure is REMOVED, red "mail retrieved" LED is enabled.
// 4. LED is disabled 5 minutes after mail has been removed if
// no more mail is placed into box (accounts for outgoing mail).

const int photoPin = 11; // use pin 11 for photoresistor
const int pressurePin = 12; // use pin 12 for pressure sensor
// rgb led requires 1 pin for each color
const int redPin = 7; // use higher resistor on red!
const int greenPin = 8; //use regular resistor on green
const int bluePin = 9; // use regular resistor on blue
int photoState = 0; // variable for photoresistor state
int pressureState = 0; // variable for pressure sensor state
int mailPresent = 0; // variable for mail presence
char color = "c"; // variable for color code for rgb led

void setup() { // pin setup (hardware)
  pinMode(photoPin, INPUT); // photoresistor is input
  pinMode(pressurePin, INPUT); // pressure sensor is input
  pinMode(redPin, OUTPUT); // led pins are all output
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
  Serial.begin(9600); // enable serial output for debugging
}

void ledColor(color) {
  switch (color) {
    case "c":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 0);
      break;
    case "r":
      digitalWrite(redPin, 255);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 0);
      break;
    case "g":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 255);
      digitalWrite(bluePin, 0);
      break;
    case "b":
      digitalWrite(redPin, 0);
      digitalWrite(greenPin, 0);
      digitalWrite(bluePin, 255);
      break;
  }
}

void loop() {
  photoState = digitalRead(photoPin); // box open?
  if (photoState > 0) { // box is open
    Serial.println("Mailbox has been opened");
    ledColor("b");
    delay(30000); // wait 30 seconds for mail
    pressureState = digitalRead(pressurePin);
    if (pressureState > 0) { // mail is present
      ledColor("g");
      mailPresent = 1;
      delay(30000); // wait 30 seconds for box to be closed
    }
    else {
      ledColor("r");
      delay(300000); // stay red for 5 minutes
      ledColor("c");
    }
    photoState = 0;
  }
  else if (mailPresent = 0) {
    ledColor("c");
  }
}
  

Again, I'm very new at this. I'm much more comfortable with Python and BASH than C/Wiring.

EDIT: Oh, and be sure to read "color" as "colour" =-)
« Last Edit: December 22, 2010, 10:03:35 am by mrbug » Logged

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A switch statement can use an ENUM, OK it are no strings but an integer in disguise smiley-wink You could do something like:

Code:
enum Color { UNDEF, RED, ORANGE, YELLOW, GREEN,  BLUE, PURPLE };

void setup()
{
  Color clr = RED;
  
  switch (clr)
  {
    case UNDEF: break;
    case RED: clr = BLUE; break;
    case BLUE: clr = YELLOW; break;    
    // etc
    default: break;
  }
}

void loop()
{
}
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I just tried that, but it doesn't seem to fit what I'm trying to do -- but I could just be reading your example incorrectly.

I want to send output to the pins to change the color of the rgb led. I figured that a function would be the best way to avoid duplicating code (thus keeping the sketch size low).

Is the setup() function the correct place for what I'm trying to do?
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Code:
case "g":
You can't have a string as a case selector. See reply #1.
Code:
case 'g':
You can have a character.
« Last Edit: December 22, 2010, 10:57:20 am by AWOL » Logged

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Got it!!

Switching all of the double quotes to single quotes and then modifying the first line of my function fixed it!

I now have
Code:
char ledColor(char color) {
instead of
Code:
void ledColor(char color) {


Thanks, everyone!


EDIT: Oops, I typed "var" instead of "void" in the second code section.
« Last Edit: December 22, 2010, 02:12:38 pm by mrbug » Logged

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Quote
I now have
Code:
char ledColor(char color) {
What does ledColor return?
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Nothing, the function (in theory) acts like this:

>> ledColor('b');
<< case 'b':
<< digitalWrite(redPin, 0);
<< digitalWrite(greenPin, 0);
<< digitalWrite(bluePin, 255);

(where each pin controls one leg of the rgb led)

It didn't like when I used "void" even though it doesn't return anything.
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Code:
char ledColor(char color) {
idea : you could return the previous value of ledColor.
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Ah yeah, I could do that for logging and logic purposes. Something like
Quote
current state: blue
previous state: red
which would show that it did not have mail before, so it's likely to have it now. That or someone is just checking it to see if there is any mail even though the led says otherwise =-)
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It didn't like when I used "void" even though it doesn't return anything.
Why? There is no reason not to declare the return type as void if it doesn't return anything. In fact, if warnings were not turned off, you would see the compiler complain that the function does not return anything if its type is not void.
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That's what was puzzling about it! Even though it did not return anything, the compiler would complain if I used void. It works with char, though, so I'm just going to leave it as it is.
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