void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);  // LED on pin 13 of UNO
}

void loop() {
  char rx_byte;
  
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();
    if (rx_byte == 'a' || rx_byte == 'A') {
      digitalWrite(13, HIGH);
    }
    else {
      digitalWrite(13, LOW);
    }
  }
}

if (rx_byte == 'a' || rx_byte == 'A') {
  digitalWrite(13, HIGH);
}

if ((rx_byte == 'a') || (rx_byte == 'b') || (rx_byte == 'c')) {
  digitalWrite(13, HIGH);
}

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);  // LED on pin 13 of UNO
}

char first_char = 0;

void loop() {
  char rx_byte;
  
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // read the character
    if ((first_char == 'c') && (rx_byte == 'd')) {
      digitalWrite(13, HIGH);
    }
    else {
      first_char = rx_byte;        // save the character for next comparison
      digitalWrite(13, LOW);
    }
  }
}

 if ((first_char == 'c') && (rx_byte == 'd')) {
  digitalWrite(13, HIGH);
}

int x = 0;
if(!x) {
	// if not x - if x evaluates to false, code here will run
}

// this code is another way of writing the above code
if (x == 0) {
}

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);  // LED on pin 13 of UNO
}

void loop() {
  char rx_byte;
  
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // read the character
    if (!(rx_byte == 'a')) {
      digitalWrite(13, HIGH);
    }
    else {
      digitalWrite(13, LOW);
    }
  }
}

if (!(rx_byte == 'a')) {
  digitalWrite(13, HIGH);
}

if (rx_byte != 'a') {
  digitalWrite(13, HIGH);
}

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);  // LED on pin 13 of UNO
}

char rx_byte = 0;

void loop() {
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();
  
    switch (rx_byte) {
      case '1':
        digitalWrite(13, HIGH);
        Serial.println("LED is ON");
      break;
      
      case '2':
        digitalWrite(13, LOW);
        Serial.println("LED is OFF");
      break;
      
      case '3':
        Serial.println("------- MENU -------");
        Serial.println("1. Switch LED on.");
        Serial.println("2. Switch LED off.");
        Serial.println("3. This menu.");
        Serial.println("--------------------");
      break;
      
      default:
        Serial.println("Invalid option");
      break;
    } // end: switch (rx_byte)
  } // end: if (Serial.available() > 0)
}

condition ? first_expression : second_expression;

int val1, val2, result;

void setup() {
  Serial.begin(9600);
  
  // change the values of val1 and val2 to see what the
  // conditional expression does
  val1 = 2;
  val2 = 5;
  // if val1 is bigger than val2, return val1
  // else if val1 is less than val2, return val2
  result = (val1 > val2) ? val1 : val2;
  
  // show result in serial monitor window
  Serial.print("The bigger number is: ");
  Serial.println(result);
}

void loop() {
}

val1 = 12;
val2 = 5;

void DashedLine()
{
    Serial.println("----------------");
}

void setup() {
  Serial.begin(9600);
  
  DashedLine();
  Serial.println("| Program Menu |");
  DashedLine();
}

void loop() {
}

void DashedLine()
{
  Serial.println("----------------");
}

 void setup() {
  Serial.begin(9600);
  
  // draw the menu box
  DashedLine(24);
  Serial.println("| Program Options Menu |");
  DashedLine(24);
}

void loop() {
}

void DashedLine(int len)
{
  int i;
  
  // draw the line
  for (i = 0; i < len; i++) {
    Serial.print("-");
  }
  // move the cursor to the next line
  Serial.println("");
}

DashedLine(24);  // passing a value of 24 to the function

void DashedLine(int len)
{
  int i;
  
  // draw the line
  for (i = 0; i < len; i++) {
    Serial.print("-");
  }
  // move the cursor to the next line
  Serial.println("");
}

void DashedLine(int len)

void setup() {
    float area;
  
    Serial.begin(9600);
    // calculate the area of a circle with radius of 9.2
    area = CircleArea(9.2);
    Serial.print("Area of circle is: ");
    // print area to 4 decimal places
    Serial.println(area, 4);
}

void loop() {
}

// calculate the area of a circle
float CircleArea(float radius)
{
    float result;
    
    result = 3.141592654 * radius * radius;
    
    return result;
}

A = π × r²
OR
A = π × r × r

Where:
A = area of the circle
π = PI = 3.141592654
r = radius of the circle

float CircleArea(float radius)

return result;

A = π × r × r

Becomes:

result = 3.141592654 * radius * radius;

 area = CircleArea(9.2);

void setup() {
    Serial.begin(9600);
    Serial.print("Area of circle is: ");
    // print area to 4 decimal places
    Serial.println(CircleArea(9.2), 4);
}

void loop() {
}

// calculate the area of a circle
float CircleArea(float radius)
{
    return (3.141592654 * radius * radius);
}

return (3.141592654 * radius * radius);

Serial.println(CircleArea(9.2), 4);

void setup() {
  int my_array[5];     // an array with 5 integer elements
  int i;               // used as an index into the array
  
  Serial.begin(9600);
  
  my_array[0] = 23;    // assign a value of 23 to the 1st element
  my_array[1] = 1001;  // assign a value of 1001 to the 2nd element, etc.
  my_array[2] = 9;
  my_array[3] = 1234;
  my_array[4] = 987;
  
  // display each number from the array in the serial monitor window
  for (i = 0; i < 5; i++) {
    Serial.println(my_array[i]);
  }
}

void loop() {
}

int my_array[5];     // an array with 5 integer elements

my_array[0] = 23;
my_array[1] = 1001;
my_array[2] = 9;
my_array[3] = 1234;
my_array[4] = 987;

 for (i = 0; i < 5; i++) {
  Serial.println(my_array[i]);
}

(my_array[i]);

void setup() {
  int my_array[5] = {23, 1001, 9, 1234, 987};
  int i;
  
  Serial.begin(9600);
  
  // display each number from the array in the serial monitor window
  for (i = 0; i < 5; i++) {
    Serial.println(my_array[i]);
  }
}

void loop() {
}

int my_array[] = {23, 1001, 9, 1234, 987};

void setup() {
  char my_str[6];    // an array big enough for a 5 character string
  
  Serial.begin(9600);
  
  my_str[0] = 'H';  // the string consists of 5 characters
  my_str[1] = 'e';
  my_str[2] = 'l';
  my_str[3] = 'l';
  my_str[4] = 'o';
  my_str[5] = 0;    // 6th array element is a null terminator
  
  Serial.println(my_str);
}

void loop() {
}

void setup() {
  char my_str[] = "Hello";
  
  Serial.begin(9600);
  
  Serial.println(my_str);
}

void loop() {
}

'w'

"This is a string"

void setup() {
  char like[] = "I like coffee and cake";  // create a string
  
  Serial.begin(9600);
  
  // (1) print the string
  Serial.println(like);
  
  // (2) delete part of the string
  like[13] = 0;
  Serial.println(like);
  
  // (3) substitute a word into the string
  like[13] = ' ';  // replace the null terminator with a space
  like[18] = 't';  // insert the new word
  like[19] = 'e';
  like[20] = 'a';
  like[21] = 0;    // terminate the string
  Serial.println(like);
}

void loop() {
}

void setup() {
  char str[] = "This is my string";  // create a string
  char out_str[40];                  // output from string functions placed here
  int num;                           // general purpose integer
  
  Serial.begin(9600);
  
  // (1) print the string
  Serial.println(str);
  
  // (2) get the length of the string (excludes null terminator)
  num = strlen(str);
  Serial.print("String length is: ");
  Serial.println(num);
  
  // (3) get the length of the array (includes null terminator)
  num = sizeof(str);  // sizeof() is not a C string function
  Serial.print("Size of the array: ");
  Serial.println(num);
  
  // (4) copy a string
  strcpy(out_str, str);
  Serial.println(out_str);
  
  // (5) add a string to the end of a string (append)
  strcat(out_str, " sketch.");
  Serial.println(out_str);
  num = strlen(out_str);
  Serial.print("String length is: ");
  Serial.println(num);
  num = sizeof(out_str);
  Serial.print("Size of the array out_str[]: ");
  Serial.println(num);
}

void loop() {
}

 void setup() {
  String my_str = "This is my string.";
  
  Serial.begin(9600);
  
  // (1) print the string
  Serial.println(my_str);
  
  // (2) change the string to upper-case
  my_str.toUpperCase();
  Serial.println(my_str);
  
  // (3) overwrite the string
  my_str = "My new string.";
  Serial.println(my_str);
  
  // (4) replace a word in the string
  my_str.replace("string", "Arduino sketch");
  Serial.println(my_str);
  
  // (5) get the length of the string
  Serial.print("String length is: ");
  Serial.println(my_str.length());
}

void loop() {
}

String my_str = "This is my string.";

int my_var = 102;

my_str.toUpperCase();

my_str = "My new string.";

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

char rx_byte = 0;

void loop() {
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // get the character
  
    // check if a number was received
    if ((rx_byte >= '0') && (rx_byte <= '9')) {
      Serial.print("Number received: ");
      Serial.println(rx_byte);
    }
    else {
      Serial.println("Not a number.");
    }
  } // end: if (Serial.available() > 0)
}

if (Serial.available() > 0) {    // is a character available?
}

rx_byte = Serial.read();       // get the character

if ((rx_byte >= '0') && (rx_byte <= '9')) {
}

if ((rx_byte >= 48) && (rx_byte <= 57)) {
}

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

char rx_byte = 0;

void loop() {
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // get the character
  
    // check if a number was received
    if ((rx_byte >= '0') && (rx_byte <= '9')) {
      Serial.print("Number received: ");
      Serial.println(rx_byte);
    }
    else if (rx_byte == '\n') {
      Serial.println("Newline");
    }
    else {
      Serial.println("Not a number.");
    }
  } // end: if (Serial.available() > 0)
}

else if (rx_byte == '\n') {

void setup() {
  Serial.begin(9600);
  Serial.println("Enter your name.");
}

char rx_byte = 0;
String rx_str = "";

void loop() {
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // get the character
    
    if (rx_byte != '\n') {
      // a character of the string was received
      rx_str += rx_byte;
    }
    else {
      // end of string
      Serial.print("Welcome ");
      Serial.println(rx_str);
      rx_str = "";                // clear the string for reuse
      Serial.println("");
      Serial.println("Enter your name.");
    }
  } // end: if (Serial.available() > 0)
}

 if (rx_byte != '\n') {
  // a character of the string was received
  rx_str += rx_byte;
}

rx_str += rx_byte;

rx_str = rx_str + rx_byte;

void setup() {
  Serial.begin(9600);
  Serial.println("Enter a number to multiply by 2.");
}

char rx_byte = 0;
String rx_str = "";
boolean not_number = false;
int result;

void loop() {
  if (Serial.available() > 0) {    // is a character available?
    rx_byte = Serial.read();       // get the character
    
    if ((rx_byte >= '0') && (rx_byte <= '9')) {
      rx_str += rx_byte;
    }
    else if (rx_byte == '\n') {
      // end of string
      if (not_number) {
        Serial.println("Not a number");
      }
      else {
        // multiply the number by 2
        result = rx_str.toInt() * 2;
        // print the result
        Serial.print(rx_str);
        Serial.print(" x 2 = ");
        Serial.print(result);
        Serial.println("");
        Serial.println("Enter a number to multiply by 2.");
      }
      not_number = false;         // reset flag
      rx_str = "";                // clear the string for reuse
    }
    else {
      // non-number character received
      not_number = true;    // flag a non-number
    }
  } // end: if (Serial.available() > 0)
}