Im having trouble concatenating a string with an int

Question

I have the below code to read a light sensor, convert to lux, concat with "lux." and send it to my SmartThings cloud. Ultimately I want a value sent to SmartThings formatted like lux.110

void checkLux() { 
  float logLux = analogRead(lightPIN) * logRange / rawRange;
  int luxValue = pow(10, logLux); 
  String statusUpdate = "lux." + luxValue; 
  Serial.println(statusUpdate);
  smartthing.send(statusUpdate); 
  delay(1000);
}

This above code spits out some weird combination of characters to the serial monitor and doesnt print lux. or the luxvalue. If I add this line String luxString = "lux."; and modify the line below, it all works great. Any thoughts on why I need to declare this string separately. According to the documentation either should work fine.

Also if there are any suggestions on variable savings within this block of code. I am not that great at it yet.

You can use concat function. statusUpdate.concat(luxValue) Doesnt that solve your problem? — ahaltindis
– ahaltindis, Commented Oct 26, 2014 at 19:57
@ahaltindis That's an answer, put it in the answers section. — Lee Fogg
– Lee Fogg, Commented Oct 26, 2014 at 23:18

Lee Fogg · Accepted Answer · 2014-10-26 23:26:08Z

3

As Arduino just uses C++ most C++ functions will also work so dont just limit yourself to Arduino's reference pages.
Apparently the String constructor doesn't support numbers, you must convert them using the String() function first as seen here.
Alternatively I think you can append a string like this:

String statusUpdate = "lux.";
statusUpdate += luxValue;

as seen here,
which is the same as using String's concat function.

statusUpdate.concat(luxValue);

answered Oct 26, 2014 at 23:26

Lee Fogg

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