structure
The basic structure of the Arduino programming language is fairly simple and runs in at least two parts. These two required parts, or functions, enclose blocks of statements.
void setup()
{
statements;
}
void loop()
{
statements;
}
Where setup() is the preparation, loop() is the execution. Both functions are required for the program to work.
The setup function should follow the declaration of any variables at the very beginning of the program. It is the first function to run in the program, is run only once, and is used to set pinMode or initialize serial communication.
The loop function follows next and includes the code to be executed continuously – reading inputs, triggering outputs, etc. This function is the core of all Arduino programs and does the bulk of the work.
setup()
The setup() function is called once when your program starts. Use it to initialize pin modes, or begin serial. It must be included in a program even if there are no statements to run.
void setup()
{
pinMode(pin, OUTPUT); // sets the 'pin' as output
}
loop()
After calling the setup() function, the loop() function does precisely what its name suggests, and loops consecutively, allowing the program to change, respond, and control the Arduino board.
void loop()
{
digitalWrite(pin, HIGH); // turns 'pin' on
delay(1000); // pauses for one second
digitalWrite(pin, LOW); // turns 'pin' off
delay(1000); // pauses for one second
}
functions
A function is a block of code that has a name and a block of statements that are executed when the function is called. The functions void setup() and void loop() have already been discussed and other built-in functions will be discussed later.
Custom functions can be written to perform repetitive tasks and reduce clutter in a program. Functions are declared by first declaring the function type. This is the type of value to be returned by the function such as 'int' for an integer type function. If no value is to be returned the function type would be void. After type, declare the name given to the function and in parenthesis any parameters being passed to the function.
type functionName(parameters)
{
statements;
}
The following integer type function delayVal() is used to set a delay value in a program by reading the value of a potentiometer. It first declares a local variable v, sets v to the value of the potentiometer which gives a number between 0-1023, then divides that value by 4 for a final value between 0-255, and finally returns that value back to the main program.
int delayVal()
{
int v; // create temporary variable 'v'
v = analogRead(pot); // read potentiometer value
v /= 4; // converts 0-1023 to 0-255
return v; // return final value
}
{} curly braces
Curly braces (also referred to as just "braces" or "curly brackets") define the beginning and end of function blocks and statement blocks such as the void loop() function and the for and if statements.
type function()
{
statements;
}
An opening curly brace { must always be followed by a closing curly brace }. This is often referred to as the braces being balanced. Unbalanced braces can often lead to cryptic, impenetrable compiler errors that can sometimes be hard to track down in a large program.
The Arduino environment includes a convenient feature to check the balance of curly braces. Just select a brace, or even click the insertion point immediately following a brace, and its logical companion will be highlighted.
