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LESSON 04 – VARIABLES
STORAGE In programming, we often
need to calculate a value, then hold on to it until we need it later on. Variables
allow us to store values inside programs.
TYPES OF VARIABLES Some programming
languages, including Arduino’s, require that we specify the type of data that
has to be stored. We do this by
creating a variable of the corresponding type. Here are some of the basic types: int – stores an integer
(whole number) float – stores a number
that contains decimals string – stores a sequence
of characters such as a word DECLARING A VARIABLE Declaring a variable
simply means announcing to the program that we will be using said
variable. Each variable always has to
be declared before being used. The following declares an integer
variable called count: int
count; The following declares a
float variable called soda: float
soda; VARIABLE NAMES There are a few simple
rules for naming variables:
Here are a few good
examples:
Here are a few bad
examples:
ASSIGNING VALUES We can assign a value to variable. Here is an example that
first declares a varable and then assigns it a value: int maxVoltage; maxVoltage = 5; We can also do the above
in a single line: int maxVoltage = 5; We must assign a value of
the same type to a variable. So we
cannot assign 5.5 to an integer variable.
OUTPUTTING VARIABLES TO
SERIAL MONITOR We’ve
already seen how to output a message to the Serial Monitor. We can also output the value of a variable. Here
is an example that creates a variable, gives it a value and outputs that
value to the Serial Monitor: int value = 10; Serial.println(value); Note
that the bottom line only works if you’ve established a connection between
the Arduino and the computer by using the Serial.begin(9600); statement. ARITHMETIC EXPRESSIONS We
can assign arithmetic expressions to variables. The
following example creates two variables and gives them values. Then, a third variable is given the sum of
the first two variables. float a = 5.2; float b = 4.3; float c = a + b; Here’s
another example with expressions: int x = 1; int y = 2; int z = 3; int product = x
* y * z; RIGHT SIDE FIRST When
the Arduino encounters a line of code that has an arithmetic expression, it
calculates the value of the expression and then continues with the work of
that line. This
means that one can have a variable that appears on both sides of the = sign. An
example of this is when you want to increment a value of a variable by
1. The statement below increments
variable x by 1. x = x + 1; GLOBAL VARIABLES Variables
that are declared inside of a function only exist within that function. So you cannot declare a variable inside the
setup function and then use it inside the loop function. If
you do wish to use a variable inside different functions, then you can
declare the variable at the very top of the program above the functions. Then, that variable will exist inside all
functions. Here’s
a general example: int value; void setup() {
//you can access value inside here } void loop() {
//you can access value inside here as well } DELAYS We
can make the Arduino wait for an amount of time by using the delay() command. We
specify the amount of time in milliseconds. Here
is the delay command halting the Arduino for 2 seconds: delay(2000); |
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TRY THIS… PRACTICE PROGRAM 03 Write a program that
creates 5 int variables a, b, c, d and e.
It then assigns them a value.
You pick the values. It then
calculates and outputs the sum and the product of those variables. Note that you may wish to create variables
that represent the sum and products. PRACTICE PROGRAM 04 Write a program will
declare a variable called x inside the setup function. On the next line, initialize x to 10. Add the lines needed to display the value
of x on the serial monitor. Alterations a) Inside the
loop() function, try incrementing the value of x and then outputting it to
screen. Note that to do this, x needs
to be a global variable. b) Add a delay of 1 second (1000 milliseconds) between
the increments. c) The Serial.print() and Serial.println() commands have
the option of converting a provided integer number to either binary or
hex. If you want to output the number
72 in binary, you use: Serial.print(72,BIN); Serial.print(value, HEX); Change
your code to output the value of x, its equivalent in binary and its
equivalent in hex. The output should
look like this: 0 -> 0 -> 0 1 -> 1 -> 1 2 -> 10 -> 2 3 -> 11 -> 3 4 -> 100 -> 4 … 9 -> 1001 -> 9 10 -> 1010 -> A 11 -> 1011 -> B … and so on… |