Page 57 - Programming the Photon Getting Started With the Internet of Things

delay(1000);
digitalWrite(LED, LOW);

delay(1000);
}

The setup function in our sketch calls one built-in function called pinMode. The function

pinMode is used to set a particular pin to be either an input or an output. So with this in
mind it is clear that we need to initially set our LED to be an output, which will also let us
use the function digitalWrite later on. The pinMode is always used in the setup function

because we only need to set the pin mode once in our sketch. The program would still
work if you called this in the loop function, but for best coding practices it is always best

to keep things that you call once in the setup function—then you know where everything
is that you only call once.

Variables

A variable is a place in the memory to store a piece of data. It has a name, a value, and a
type. For example, the following statement declares the pin number:

int pin = D0;

This code creates a variable called pin whose value is D0, and its type is int. Later on in

your program you can refer to this variable by its name, at which point its value will be
looked up and used. For example:

pinMode(pin, OUTPUT);

It is the value of the pin that will be passed into the pinMode() function. In this particular
case you don’t actually need to use a variable; this statement would work just as well if
you referenced the pin number directly:

pinMode(D0, OUTPUT);

The advantage of a variable in this case is that you only need to specify the actual number
of the pin once, but it has a huge advantage in that you can use this more than once in your
code. When naming your variable you can also use a descriptive name, which will make
the significance of the variable clearer (e.g., a program controlling some LEDs might have
variables called redPin, GreenPin, etc.).

A variable has other advantages over a value like a number. You can change the value
of a variable using an assignment (indicated by an equal sign). For example:

pin = D1;

This will change the value of the variable to D1. You can see that we don’t actually