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Topic: [SOLVED] switch case with strings (Read 15611 times) previous topic - next topic

mrbug

Dec 22, 2010, 03:10 pm Last Edit: Dec 22, 2010, 05:17 pm by mrbug Reason: 1
I'm trying to control a single RGB LED using a switch case, but I keep getting this error:
Code: [Select]
error: case label does not reduce to an integer constant

My code looks like this:
Code: [Select]

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: [Select]
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?

PaulS

#1
Dec 22, 2010, 03:14 pm Last Edit: Dec 22, 2010, 03:16 pm by PaulS Reason: 1
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: [Select]
void ledColor(char color) {

Code: [Select]
ledColor("blue");
"blue" is not a character. It is an array of characters.

mrbug

#2
Dec 22, 2010, 03:44 pm Last Edit: Dec 22, 2010, 03:58 pm by mrbug Reason: 1
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: [Select]
error: case label does not reduce to an integer constant
and
Code: [Select]
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: [Select]
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?

Groove

Psst, we can't see your code.
Per Arduino ad Astra

mrbug

#4
Dec 22, 2010, 04:02 pm Last Edit: Dec 22, 2010, 04:03 pm by mrbug Reason: 1
Ah, good point. Here you go:

Code: [Select]
// 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" =-)

robtillaart


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

Code: [Select]

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()
{
}

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

mrbug

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?

AWOL

#7
Dec 22, 2010, 04:55 pm Last Edit: Dec 22, 2010, 04:57 pm by AWOL Reason: 1
Code: [Select]
case "g":
You can't have a string as a case selector. See reply #1.
Code: [Select]
case 'g':
You can have a character.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

mrbug

#8
Dec 22, 2010, 05:17 pm Last Edit: Dec 22, 2010, 08:12 pm by mrbug Reason: 1
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: [Select]
char ledColor(char color) {
instead of
Code: [Select]
void ledColor(char color) {


Thanks, everyone!


EDIT: Oops, I typed "var" instead of "void" in the second code section.

PaulS

Quote
I now have
Code:
char ledColor(char color) {

What does ledColor return?

mrbug

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.

robtillaart

Code: [Select]
char ledColor(char color) {
idea : you could return the previous value of ledColor.
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

mrbug

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 =-)

PaulS

Quote
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.

mrbug

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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