Simple Arduino Serial Communication

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//The code belongs to the following tutorial video: https://youtu.be/feAcAiexzkM

bool enablerun = false;
bool newData = false;
String sin1, sin2; //sin = Serial INput
float num1, num2; //num = number
char receivedCommand; //received character as a command
int cycles = 0;

void setup()
{
  Serial.begin(9600); //define baud rate
  Serial.println("Testing Serial Commands"); //print a message


  Serial.println("m = mirror");
  Serial.println("a = add two numbers");
  Serial.println("c = count");
  Serial.println("d = send formatted data");
  Serial.println("s = stop sending data");
  Serial.println("----------------------------");
}

void loop()
{
  //Comment out one of these below. Either use the Switch-Case or the if()
  CheckSerialSwitchCase(); //This is with Switch - Case

  //CheckSerialIF(); //This is with IF()
  //---------------------------------------------------


  sendFormattedData(); //This is a function

}


void CheckSerialIF() //Checking the serial port via IF statements
{
  if (Serial.available() > 0) //if something comes from the Serial. This part only checks the serial.
  {
    receivedCommand = Serial.read(); // this will read the command character
    newData = true; //this creates a flag and says there's a data coming
  }

  if (newData == true) //if we received something (see above)
  {

    if (receivedCommand == 'm') //this is the mirror part
    {
      sin1 = Serial.readString(); //Read one serial input

      Serial.print("Message was: ");
      Serial.println(sin1);

    }

    if (receivedCommand == 'a') //addition
    {
      //example: a 42 1
      while (!Serial.available());
      num1 = Serial.parseFloat();

      num2 = Serial.parseFloat();

      addTwoNumbers(num1, num2);

    }

    if (receivedCommand == 'c') //Counting
    {
      //example: c 5
      while (!Serial.available());
      num1 = Serial.parseFloat();

      counterCode(num1);

    }

    if (receivedCommand == 'd') //Sending formatted data
    {
      enablerun = true; // this enables the function for sending formatted data
    }


    if (receivedCommand == 's') //immediately stops the code
    {
      enablerun = false;
      Serial.println("Stopped!");

    }

  }
  //after we went through the above tasks, newData becomes false again, so we are ready to receive new commands again.
  newData = false;
}

void CheckSerialSwitchCase() //Checking the serial port via Switch-Case
{
  if (Serial.available()) { //If there are bytes/characters coming through the serial port

    char commandcharacter = Serial.read(); //read the character for the command

    switch (commandcharacter) { //we read a character which can

    case 'm': //m = "mirror"; we send back the received stuff

      sin1 = Serial.readString(); //Read one serial input

      Serial.print("Message was: ");
      Serial.println(sin1);

      break;

    case 'a': //a = "addition"; we add two numbers
      //example: a 42 1
      while (!Serial.available());

      num1 = Serial.parseFloat();

      num2 = Serial.parseFloat();

      addTwoNumbers(num1, num2);

      break;


    case 'c': //c as count
      //example: c 5
      while (!Serial.available());

      num1 = Serial.parseFloat();

      counterCode(num1);
      break;


    case 'd': //we request formatted data

      enablerun = true; // this enables the function for sending formatted data

    break;

    case 's': //s = stop; we make enablerun false, so we stop receiving data.

      enablerun = false;
      Serial.println("Stopped!");

    break;
    }
  }
}


void addTwoNumbers(float sin1, float sin2)//This function adds two numbers and prints it on the serial
{
  float result; //create a variable for storing the result

  result = num1 + num2; //adding the two numbers

  Serial.print("The result is: "); //text
  Serial.println(result); //result

  return;
}

void counterCode(double num1) //We count until a certain number and in every second we print a number
{
  for(int i = 0; i<num1; i++)
  {
    delay(1000); //wait a second
    Serial.print(i+1);
    Serial.println(" seconds elapsed");
  }
  Serial.println("Done!");
  return;
}

void sendFormattedData()// we create a random series of data which will be transferred to the serial terminal formatted
{


  if (enablerun == true)
  {
    Serial.print(cycles);  //we just print an increasing integer

    Serial.print('\t'); //separate it with a tab

    Serial.print(millis()); //we print some increasing number, such as the cpu's time

    Serial.print('\t'); //separation

    Serial.print(millis() * 3); //some number which increases proportional to the time

    Serial.println(); //new line

    //expected output format: 1 1000  3000

    delay(1000); //waiting a second
    cycles++; //increase the number of loops
  }

}