7

FORGE

void push(int item) {
if (top == MAXSTACK)
top = 0;
ourList[top++] = item;
}
int peek(int x) {
return ourList[(top + x) % MAXSTACK];
}
};
This stack is a list of data that we can keep pushing
data to, and peeking at data in. It will always hold the
most recent 128 datapoints pushed into the stack.
Our stack is implemented within a class. We
discussed classes in the previous tutorial when we
used one to access the DHT11, but in the above code
we’re creating our own. Classes, a little like stacks,
are a huge subject that can even dictate the design of
an entire programming language, but they’re basically
just a way of co-locating data with the functions that
use the data. In our case, that means the data is the
value for each temperature reading, and the functions
add and read values from the stack. If the data and
functions are solely for the use of the class, they’re
defined beneath a ‘private’ specifier, and won’t be
accessible outside the class – this helps hide the
complexity and avoids erroneous access from outside
the class. Conversely, for data and functions intended
to be accessed by you, the programmer, we use
the ‘public’ specifier. In our above class, the push

and peek functions are all public, as we’ll be using

these to create and view our stack. The array

that holds the temperature readings,

ourList, is private, as too is an

integer that holds the

current top array

position of

the stack.

There are

three functions

that are members

of this class. The

first is special because

it takes the name of the

class itself – Stack(). This

is the constructor, and like

setup() in an Arduino project,

it runs automatically when a

class is instantiated. We use this

instantiation to set the internal values

to zero, including every element of the

array. This safeguards against wayward

values being left over in memory or a

previous execution. Although we’ve not used

it here, the opposite function to the constructor

is the destructor, written as ~Stack() in a class

definition, and this function is run when a class is

deleted. As our code only quits when the Arduino is

reset or powered off, we’re saving space and not

If you experience

display problems,

you may need to

use an external 5 V

power source for the

screen, connecting

the common ground

to the Arduino.

QUICK TIP

Above

SSD1306-compatible

screens are cheap

and readily available,

and can even be

found in different

colours and in

multiple colour

configurations

Left

The OLED display

and temperature

sensor in situ on

the breadboard