Arduino Basics : functions

When we create a function, it must be given a name. The naming convention for functions is the same as for variables:

• The function name can be made up of alphanumeric characters (A to Z; a to z; 0 to 9) and the underscore (_).
• The function name may not start with a number
• A function name must not be used that is the same as a language keyword or existing function.

A function must have a return type. If teh example function does not return anything, it will have a return type of void.

The function body is made up of a variety of statements placed between braces {}.

1. each function must have a unique name,
2. the function name is followed by parentheses ()
3. functions have a return type, e.g. void,
4. the body of a function is enclosed in opening and closing braces {}.

To call the function, you use the function name followed by opening and closing parentheses and then put a semi colon after it.

There are advantages of using functions is that they avoid having to write the same code over and over again. Every time you call a function, we are just reusing code that has been written once.

If you were to write code that say performed the same task 5 times then if you wished to update this for some reason you would have to modify the code in 5 places but if you were to use a function and call it 5 times then all you have to do is modify the function.

Functions can be used to break a sketch up into pieces which make it easier to understand

There are 2 ways you can declare a function

Arduino Example 1

Let’s look at a very simple function which simply adds 2 numbers

int sum_function (int x, int y) // function declaration 
{
   int z = 0;
   z = x + y;
   return z; // return the value
}

void setup () 
{
  Serial.begin(9600);
  int result = 0;
  result = sum_function (9,4); //our function
  Serial.print(result); //display via serial monitor
}

void loop () 
{
}

In the serial monitor window, you will see something like this

13

Arduino Example 2

The second way is to define  a function and then declare it after the loop, lets see the example above written like that

int sum_function (int , int ); // function definition 

void setup () 
{
  Serial.begin(9600);
  int result = 0;
  result = sum_function (9,4); //our function
  Serial.print(result); //display via serial monitor
}

void loop () 
{
}

int sum_function (int x, int y) // function declaration 
{
   int z = 0;
   z = x + y;
   return z; // return the value
}

When you run this you will see the same result as before in the serial monitor window

13

Arduino Example : RGB LED

Using an RGB led to let’s see how we can use some functions in this example

Here is the circuit for reference

We will switch the various red, green and blue led’s on and switch the off – these will all be functions

int redled = 11;
int blueled = 10;
int greenled = 9;


void setup() 
{
  pinMode(redled, OUTPUT); //set the LED pin as an output
  pinMode(blueled, OUTPUT); //set the LED pin as an output
  pinMode(greenled, OUTPUT); //set the LED pin as an output
}

void loop() 
{
int i = 1;
AllOff(); //AllOff function called
delay(1000);

  while(i<=3)
  {
    switch (i) 
    {
    case 1:
      RedOn(); //RedOn function called
      delay(1000);
      break;
    case 2:
      BlueOn(); //BlueOn function called
      delay(1000);
      break;
    case 3:
      GreenOn(); //GreenOn function called
      delay(1000);
      break;
    default: 
      break;
    }
    i++;
  }
}

void AllOff()
{
  digitalWrite(redled, HIGH); // red led off
  digitalWrite(blueled, HIGH); //blue led off
  digitalWrite(greenled, HIGH); //green led off
}

void RedOn()
{
  digitalWrite(redled, LOW); // red led on
  digitalWrite(blueled, HIGH); //blue led off
  digitalWrite(greenled, HIGH); //green led off
}

void BlueOn()
{
  digitalWrite(redled, HIGH); // red led off
  digitalWrite(blueled, LOW); //blue led on
  digitalWrite(greenled, HIGH); //green led off
}

void GreenOn()
{
  digitalWrite(redled, HIGH); // red led off
  digitalWrite(blueled, HIGH); //blue led off
  digitalWrite(greenled, LOW); //green led on
}