Arduino C++ by Example

Basics setup and Serial Output

• setup() gets called once when you program starts

• loop() runs repeatedly again and again and again for as long as your program runs

#include <Arduino.h>

int count = 0; // Declare an integer variable called count and initialize it to 0

// the setup function runs at the very start of the program
void setup() {
	Serial.begin(9600); // Initialize the serial port
	Serial.println("Hello world!"); // Print "Hello world!" to the serial port
}

// the loop function runs again and again and again for as long as your program runs
void loop() {
	count++; // Increment the value of count by 1
	Serial.println(count); // Print the value of count
	delay(1000); // Wait for 1 sec (1000 ms) before continuing
}

Serial Input

#include <Arduino.h>

const int ledPin = 10; // LED connected to digital pin 10. `const` means the value of `ledPin` can't be changed.

void setup() {
  pinMode(ledPin, OUTPUT); // set the mode of pin ledPin to be OUTPUT
  Serial.begin(9600); // Begin a serial connection at a baud rate of 9600
	delay(2000); // wait for 2 sec (2000 ms)
	Serial.println(); // print an empty line
	Serial.println("Enter '1' to turn on the LED, '0' to turn it off: "); // print instructions
}

void loop() {
  char userChoice; // create a variable of type char (can hold a single character)
  
  while (!Serial.available()) {} // Wait for user to press any key (do nothing while Serial has no new data available)
  userChoice = Serial.read(); // Read the user input into the userChoice variable

  switch (userChoice) { // Switch according to the contents of userChoice
    case '0': // if the user entered '0'
      digitalWrite(ledPin, HIGH); // set the ledPin to HIGH (5V) 
			Serial.println("OFF"); // print "OFF"
      break; // exit out of the switch statement
    case '1': // if the user entered '1'
      digitalWrite(ledPin, LOW); // set the ledPin to LOW (0V)
			Serial.println("ON"); // print "ON"
      break; // exit out of the switch statement
		default: // if the user enterd anything else
			Serial.println("Invalid input");
			break; // exit out of the switch statement
  }
}

• ▶️ Run the program

• Open the Serial Monitor
• Make sure it’s set to 9600 baud
• Set it to No Line Ending
• Now enter 1 or 0 into the Message field, press enter to submit and watch the LED turn on or off!

More Serial Input

#include <Arduino.h>

void setup() {
  Serial.begin(9600);
	delay(2000);
}

void loop() {
  String userName = ""; // a variable of type String (can hold text), called 'userName'
  int birthYear = 0; // a variable to hold an integer number

  Serial.println();
  Serial.println("Please enter your name");

  while (!Serial.available()) {} // Wait for user input to complete
  userName = Serial.readStringUntil('\n'); // Read the user input up until we encounter a newline character!

	Serial.println("Hello " + userName + "!"); // welcome the user by name!
	
  Serial.println(); // Print a newline
  Serial.println("What year were you born?");

  while(birthYear == 0) {
    while (!Serial.available()) {} // Wait for user input to complete
    String birthYearStr = Serial.readStringUntil('\n'); // Read the user input into a temporary variable
    birthYear = birthYearStr.toInt(); // convert to integer and save into the `birthYear` variable
        
    if(birthYear == 0) { // if the user input was not a valid number, the result will be 0
      Serial.println("It looks like you entered an invalid year. Please try again!");
      continue; // abort this loop and go back to the top and start the next while loop
    }

    int ageIn2050 = 2050 - birthYear; // calulate user age in 2050
    Serial.println("In the year 2050 you'll be " + (String)ageIn2050 + " years old."); // output the result
    // note how we have to cast `ageIn2050` to a String before we can use it in text!
  }
}