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Arduino programming: Stacks, classes, and scrolling displays

SCHOOL OF MAKING

adding a destructor, but a good programmer uses

the destructor to free up any allocated memory and

generally clean up after themselves.

The push function simply checks to make sure

the top isn’t yet at the maximum stack size value,

and enters the item value at the current top position

before incrementing top to the next array location.

We haven’t implemented pop because it’s not

needed – we’re simply overwriting previous values

in the array. Instead, we have peek to return the

item value at x. The tricky part is that because top

is always changing, x is an offset from the value of

top, which we modulo against the maximum stack

size, to make sure it’s both within range and loops

over when higher. Modulo is very useful for such a

simple operator!

DRAWING LINES

The next chunk of code instantiates three types for

the sensor, our new Stack class and for the screen,

before filling out the Arduino’s setup function. This

STACK OVERFLOW

A stack is a data structure, and that just means it holds

data in a specific way. The most common stack holds

data in the same way you create a deck of cards,

putting one card on top of the next and removing cards

from the top of the pile. In stack terminology, this is a

LIFO stack – the card that was last in is first out. FIFO

(first in, first out) is another common variant, and this

operates as a basic queue. Alan Turing even coined

the terms ‘bury’ and ‘unbury’ in 1946 to describe the

process of adding and removing data from a stack, but

we now use the terms ‘push’ and ‘pop’ for the same

thing. Additionally, ‘peek’ is often used when you want

to take a look at the top card, rather than remove it,

or examine another card in the pack. Just like in 1946,

however, stacks are ideal when you only have a limited

amount of memory.

The module itself combines both temperature and

humidity sensors, and the great thing about this

module is that it’s incredibly easy to use

”

”

Right

Libraries can be

downloaded and

installed manually,

as discussed last

month, but it’s much

easier to just use the

Arduino IDE

The term ‘stack

overflow’ actually

refers to when you

try to write to the

stack and the stack

is full. Fortunately, as

ours is fixed in size,

this won’t happen.

QUICK TIP

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Pop

Pop

Pop

Pop

Pop

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Push

Push

Push

Push

Push

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