Arduino IDE "'lt' was not declared in this scope" Error

for (int a=0; a&/lt;=255;a++) //loop from 0 to 255

for (int a=255; a>=0;a--) //loop from 255 down to 0

Became something more like this...

for (int a=255; a&/gt;=0;a--) //loop from 255 down to 0

In both cases I said "something like" because the relevant section of the code appears here in the color red to make it stand out, and because the CMS for this website won't allow for the exact character strings that showed in the Arduino IDE.

As a result the IDE was seeing "lt" and "gt" as new variables that had not been declared (hence the error message 'lt' was not declared in this scope)

Fortunately the solution is simple – replacing the modified code with standard greater than/less than characters made the code work perfectly.

It also seems that you can copy the code here, from this site, and paste it directly into the Arduino IDE for Mac and it will work with no encoding issues:

const int ledPin = 9; // the pin that the LED is attached to
void setup ()
{
pinMode(ledPin, OUTPUT); // declare pin 9 to be an output:
}
void loop()
{
for (int a=0; a<=255;a++) //loop from 0 to 255
{
analogWrite(ledPin, a); // set the brightness of pin 9:
delay(8); //wait for 8 microseconds
}
for (int a=255; a>=0;a--) //loop from 255 down to 0
{
analogWrite(ledPin, a); // set the brightness of pin 9:
delay(8); //wait for 8 microseconds
}
delay(800); //wait for 800 microseconds
}

Good Learning Opportunity

This was actually a great opportunity to teach the boys a little about debugging code. We knew that we had an Arduino board and IDE that worked, we had seen it with the first (and more basic) Blink program.

That meant there was something wrong with the code for our program. We tried another, more basic, program from Sunfounder that did work, so we could assume that their code was generally good.

The next step was to look at the line flagged as an error in the Arduino IDE and compare it very carefully to the original code on the Sunfounder site, revealing the problem and the solution.