SunFounder 3in1 Kit
Declare a variable
Declaring a variable means creating a variable.
To declare a variable, you need two things: the data type, and the variable name. The data type needs to be separated
from the variable by a space, and the variable declaration needs to be terminated by a ;.
Let’s use this variable as an example.
int delayTime;
Data Type
Here int is a data type called integer type, which can be used to store integers from -32768 to 32766. It can also not
be used to store decimals.
Variables can hold different kinds of data other than integers. The Arduino language (which, remember, is C++) has
built-in support for a few of them (only the most frequently used and useful are listed here):
• float: Store a decimal number, for example 3.1415926.
• byte: Can hold numbers from 0 to 255.
• boolean: Holds only two possible values, True or False, even though it occupies a byte in memory.
• char: Holds a number from -127 to 127. Because it is marked as a char the compiler will try to match it to a
character from the .
• string: Can stores a string of characters, e.g. Halloween.
Variable Name
You can set the variable to any name you want, such as i, apple, Bruce, R2D2, Sectumsempra, but there are some
basic rules to follow.
1. describe what it is used for. Here, I named the variable delayTime, so you can easily understand what it does. It
works fine if I name the variable barryAllen, but it confuses the person looking at the code.
2. Use regular nomenclature. You can use CamelCase like I did, with the initial T in delayTime so that it is
easy to see that the variable consists of two words. Also, you can use UnderScoreCase to write the variable as
delay_time. It doesn’t affect the program’s running, but it would help the programmer to read the code if you
use the nomenclature you prefer.
3. Don’t use keywords. Similar to what happens when we type “int”, the Arduino IDE will color it to remind you
that it is a word with a special purpose and cannot be used as a variable name. Change the name of the variable
if it is colored.
4. Special symbols are not allowed. For example, space, #, $, /, +, %, etc. The combination of English letters (case
sensitive), underscores, and numbers (but numbers cannot be used as the first character of a variable name) is
rich enough.
Assign a value to a variable
Once we have declared the variable, it is time to store the data. We use the assignment operator (i.e. =) to put value
into the variable.
We can assign values to the variable as soon as we declare it.
int delayTime = 500;
It is also possible to assign a new value to it at some time.
2.3. How to build an Arduino Project 75
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