Inputting a single String/Char into Serial Monitor

Question

I'm having issues with inputting a string/character into the serial monitor, and I'm a beginner at programming therefore I don't know how to solve it.

I have an if/else statement which works like a switch case statement. I did begin with a switch case but I was developing a lot of problems with it, one being inputting a string/character (A, S, M, D, P) to point to each case. I know a switch case is for ints so I gave up and moved on to multiple if/else statements.

I have tried (in void loop()),

char theOperator = dataInput();

if (theOperator == 'A') {
  // If input is equal to 1, carry out function 'addition()'
  addition();
}

but it displays the error message I have in the 'addition' function.

Here is where the code for the input is used (globally defined),

char theOperator;

char dataInput() {
  while (!Serial.available()) {
    // Wait for the user to enter value
  }
  return Serial.parseInt();
}

I have tried similar things like Serial.read(), but this either loops the start of my program and does not allow me to input a value, or it just won't take the value at all.

Any help would be appreciated, I will post my full code below so that you might understand my program (the issue of the if/else etc is at the top).

*EDIT: Forgot to mention, I can do something like,

char theOperator = dataInput();

  if (theOperator == 1) {
    // If input is equal to 1, carry out function 'addition()'
    addition();
  }

And this works. However I want it to take A, S, M, D, or P instead of 1, 2, 3, 4, 5.

#define LED_RED 5
#define LED_ORANGE 6
#define LED_YELLOW 9
#define LED_GREEN 10
#define LED_BLUE 11

int potValue;

#define potPin A0

// Limits the range of the numbers entered to between -99 and 999
long firstNumber = constrain(firstNumber, -99, 999);
long secondNumber = constrain(secondNumber, -99, 999);
long value;

char theOperator;

char dataInput() {
  while (!Serial.available()) {
    // Wait for the user to enter value
  }
  return Serial.parseInt();
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void setup() {

  Serial.begin(9600);

  pinMode(LED_RED, OUTPUT);
  pinMode(LED_ORANGE, OUTPUT);
  pinMode(LED_YELLOW, OUTPUT);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(LED_BLUE, OUTPUT);

  pinMode(potPin, INPUT);
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void loop() {

  Serial.println ("Enter your chosen operator");
  Serial.println ("A for Addition, S for Subtraction, M for Multiplication,");
  Serial.println ("D for Division, and P for Potentiometer: ");

  // Takes an input from the user
  char theOperator = dataInput();

  if (theOperator == 'A') {
    // If input is equal to 1, carry out function 'addition()'
    addition();
  }
  else if (theOperator == 'S') {
    // If input is equal to 2, carry out function 'subtraction()'
    subtraction();
  }
  else if (theOperator == 'M') {
    // If input is equal to 3, carry out function 'multiplication()'
    multiplication();
  }
  else if (theOperator == 'D') {
    // If input is equal to 4, carry out function 'division()'
    division();
  }
  else if (theOperator == 'P') {
    // If input is equal to 5, carry out function 'potentiometer()'
    potentiometer();
  }
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void addition() {

  Serial.println ("A");
  Serial.println ("Please enter first number in format nnn: ");
  firstNumber = dataInput(); // Asks the user to input the first set of numbers

  /* Message must be in format cnnnnnn
     therefore first number must be greater than or equal to -99 and less than or equal to 999*/
  if (firstNumber >= -99 && firstNumber <= 999) {
    Serial.println (firstNumber); // Prints the first set of numbers for the user to view
  }
  else {
    /* If the data input does not match the format cnnnnnn then this error message will display
       if the input is invalid the red LED will also turn on */
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  Serial.println ("Please enter second number in format nnn: ");
  secondNumber = dataInput(); // Asks the user to input the second set of numbers

  /* Message must be in format cnnnnnn
     therefore second number must be greater than or equal to -99 and less than or equal to 999*/
  if (secondNumber >= -99 && secondNumber <= 999) {
    // The LED will turn off if it was previously on because this is a valid input
    digitalWrite(LED_RED, LOW);
    Serial.println (secondNumber); // Prints the second set of numbers for the user to view
  }
  else {
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  /* Give time for the red error LED to stay on
     for the user to notice he/she has made an invalid input */
  delay(500);
  digitalWrite(LED_RED, LOW);

  // As this case is for addition, it will add the first and second numbers
  value = (firstNumber + secondNumber);

  Serial.print("Value: ");
  // Prints the value of the two sets of numbers so that the user can see the value of their message
  Serial.println(value);

  /////// The 'sign' flag ///////
  if (value >= 1) {
    // If value is a positive number (excluding 0) turn orange LED on
    digitalWrite(LED_ORANGE, HIGH);
  }
  else if (value <= -1) {
    // If value is a negative number, turn orange LED off
    digitalWrite(LED_ORANGE, LOW);
  }
  else if (value == 0) {
    // If value is equal to 0, set orange LED at half brightness
    int brightness;
    // Changes the brightness of the LED so that it is half bright
    brightness++;
    brightness %= 128;
    analogWrite(LED_ORANGE, brightness);
  }

  /////// The 'even' flag ///////
  if ((value % 2) == 0) {
    // If the modulo is equal to 0, it's an even
    digitalWrite(LED_BLUE, HIGH);
  } else {
    // If the modulo is not equal to 0, it's an odd
    digitalWrite(LED_BLUE, LOW);
  }
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void subtraction() {

  Serial.println ("S");
  Serial.println ("Please enter the first number in format nnn: ");
  firstNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore first number must be greater than or equal to -99 and less than or equal to 999*/
  if (firstNumber >= -99 && firstNumber <= 999) {
    Serial.println (firstNumber); // Prints the first set of numbers for the user to view
  }
  else {
    /* If the data input does not match the format cnnnnnn then this error message will display
       if the input is invalid the red LED will also turn on */
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  Serial.println ("Please enter second number in format nnn: ");
  secondNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore second number must be greater than or equal to -99 and less than or equal to 999*/
  if (secondNumber >= -99 && secondNumber <= 999) {
    digitalWrite(LED_RED, LOW);
    Serial.println (secondNumber); // Prints the second set of numbers for the user to view
  }
  else {
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  /* Give time for the red error LED to stay on
     for the user to notice he/she has made an invalid input */
  delay(500);
  digitalWrite(LED_RED, LOW);

  // As this case is for subtraction, it will subtract the first and second numbers
  value = (firstNumber - secondNumber);
  Serial.print("Value: ");
  // Prints the value of the two sets of numbers so that the user can see the value of their message
  Serial.println(value);

  /////// The 'sign' flag ///////
  if (value >= 1) {
    // If value is a positive number (excluding 0) turn orange LED on
    digitalWrite(LED_ORANGE, HIGH);
  }
  else if (value <= -1) {
    // If value is a negative number, turn orange LED off
    digitalWrite(LED_ORANGE, LOW);
  }
  else if (value == 0) {
    // If value is equal to 0, set orange LED at half brightness
    int brightness;
    // Changes the brightness of the LED so that it is half bright
    brightness++;
    brightness %= 128;
    analogWrite(LED_ORANGE, brightness);
  }

  /////// The 'even' flag ///////
  if ((value % 2) == 0) {
    // If the modulo is equal to 0, it's an even
    digitalWrite(LED_BLUE, HIGH);
  } else {
    // If the modulo is not equal to 0, it's an odd
    digitalWrite(LED_BLUE, LOW);
  }
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void multiplication() {

  Serial.println ("M");
  Serial.println ("Please enter the first number in format nnn: ");
  firstNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore first number must be greater than or equal to -99 and less than or equal to 999*/
  if (firstNumber >= -99 && firstNumber <= 999) {
    Serial.println (firstNumber); // Prints the first set of numbers for the user to view
  }
  else {
    /* If the data input does not match the format cnnnnnn then this error message will display
       if the input is invalid the red LED will also turn on */
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  Serial.println ("Please enter second number in format nnn: ");
  secondNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore second number must be greater than or equal to -99 and less than or equal to 999*/
  if (secondNumber >= -99 && secondNumber <= 999) {
    digitalWrite(LED_RED, LOW);
    Serial.println (secondNumber); // Prints the second set of numbers for the user to view
  }
  else {
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  /* Give time for the red error LED to stay on
     for the user to notice he/she has made an invalid input */
  delay(500);
  digitalWrite(LED_RED, LOW);

  // As this case is for multiplication, it will multiply the first and second numbers
  value = (firstNumber * secondNumber);
  Serial.print("Value: ");
  // Prints the value of the two sets of numbers so that the user can see the value of their message
  Serial.println(value);

  /////// The 'sign' flag ///////
  if (value >= 1) {
    // If value is a positive number (excluding 0) turn orange LED on
    digitalWrite(LED_ORANGE, HIGH);
  }
  else if (value <= -1) {
    // If value is a negative number, turn orange LED off
    digitalWrite(LED_ORANGE, LOW);
  }
  else if (value == 0) {
    // If value is equal to 0, set orange LED at half brightness
    int brightness;
    // Changes the brightness of the LED so that it is half bright
    brightness++;
    brightness %= 128;
    analogWrite(LED_ORANGE, brightness);
  }

  /////// The 'even' flag ///////
  if ((value % 2) == 0) {
    // If the modulo is equal to 0, it's an even
    digitalWrite(LED_BLUE, HIGH);
  } else {
    // If the modulo is not equal to 0, it's an odd
    digitalWrite(LED_BLUE, LOW);
  }
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void division() {

  Serial.println ("D");
  Serial.println ("Please enter the first number in format nnn: ");
  firstNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore first number must be greater than or equal to -99 and less than or equal to 999
     Division by 0 is not allowed */
  if (firstNumber >= -99 && firstNumber <= 999 && firstNumber != 0) {
    Serial.println (firstNumber); // Prints the first set of numbers for the user to view
  }
  else if (firstNumber == 0) {
    /* If the data input does not match the format cnnnnnn or if the input is
       equal to 0 then this error message will display, and if the input is invalid
       the red LED will also turn on, or if the input equals to 0 the LED will flash
       and stay on at half brightness */
    blinkError();
    Serial.println ("--------------- ERROR ---------------");
  }
  else {
    digitalWrite(LED_RED, HIGH);
  }

  Serial.println ("Please enter second number in format nnn: ");
  secondNumber = dataInput();

  /* Message must be in format cnnnnnn
     therefore second number must be greater than or equal to -99 and less than or equal to 999
     Division by 0 is not allowed */
  if (secondNumber >= -99 && secondNumber <= 999 && secondNumber != 0) {
    digitalWrite(LED_RED, LOW);
    Serial.println (secondNumber); // Prints the second set of numbers for the user to view
  }
  else if (secondNumber == 0) {
    blinkError();
    Serial.println ("--------------- ERROR ---------------");
  }
  else {
    digitalWrite(LED_RED, HIGH);
    Serial.println ("--------------- ERROR ---------------");
  }

  /* Give time for the red error LED to stay on
     for the user to notice he/she has made an invalid input */
  delay(500);
  digitalWrite(LED_RED, LOW);

  // As this case is for division, it will divide the first and second numbers
  value = (firstNumber / secondNumber);
  Serial.print("Value: ");
  // Prints the value of the two sets of numbers so that the user can see the value of their message
  Serial.println(value);

  /////// The 'sign' flag ///////
  if (value >= 1) {
    // If value is a positive number (excluding 0) turn orange LED on
    digitalWrite(LED_ORANGE, HIGH);
  }
  else if (value <= -1) {
    // If value is a negative number, turn orange LED off
    digitalWrite(LED_ORANGE, LOW);
  }
  else if (value == 0) {
    // If value is equal to 0, set orange LED at half brightness
    int brightness;
    // Changes the brightness of the LED so that it is half bright
    brightness++;
    brightness %= 128;
    analogWrite(LED_ORANGE, brightness);
  }

  /////// The 'even' flag ///////
  if ((value % 2) == 0) {
    // If the modulo is equal to 0, it's an even
    digitalWrite(LED_BLUE, HIGH);
  } else {
    // If the modulo is not equal to 0, it's an odd
    digitalWrite(LED_BLUE, LOW);
  }
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void potentiometer() {

  Serial.println("P");

  do {
    if (potValue >= 0 && potValue <= 6) {
      /* If the value on the potentiometer is greater than or equal to 0,
         or less than or equal to 6, the red LED will turn on */

      potValue = analogRead(potPin); // Reads the value on the pin
      potValue = map(potValue, 0, 1023, 0, 31); // Changes the default range from 0 to 1023 to 0 to 31

      // Converts the DEC value of the potentiometer to BIN
      Serial.println(potValue, BIN);
      delay(500);

      digitalWrite(LED_RED, HIGH);
      digitalWrite(LED_ORANGE, LOW);
      digitalWrite(LED_YELLOW, LOW);
      digitalWrite(LED_GREEN, LOW);
      digitalWrite(LED_BLUE, LOW);
    }
    else if (potValue >= 7 && potValue <= 12) {
      /* If the value on the potentiometer is greater than or equal to 3,
         or less than or equal to 12, the orange LED will turn on */

      potValue = analogRead(potPin); // Reads the value on the pin
      potValue = map(potValue, 0, 1023, 0, 31); // Changes the default range from 0 to 1023 to 0 to 31

      Serial.println(potValue, BIN);
      delay(500);

      digitalWrite(LED_RED, LOW);
      digitalWrite(LED_ORANGE, HIGH);
      digitalWrite(LED_YELLOW, LOW);
      digitalWrite(LED_GREEN, LOW);
      digitalWrite(LED_BLUE, LOW);
    }
    else if (potValue >= 13 && potValue <= 18) {
      /* If the value on the potentiometer is greater than or equal to 13,
         or less than or equal to 18, the yellow LED will turn on */

      potValue = analogRead(potPin); // Reads the value on the pin
      potValue = map(potValue, 0, 1023, 0, 31); // Changes the default range from 0 to 1023 to 0 to 31

      Serial.println(potValue, BIN);
      delay(500);

      digitalWrite(LED_RED, LOW);
      digitalWrite(LED_ORANGE, LOW);
      digitalWrite(LED_YELLOW, HIGH);
      digitalWrite(LED_GREEN, LOW);
      digitalWrite(LED_BLUE, LOW);
    }
    else if (potValue >= 19 && potValue <= 24) {
      /* If the value on the potentiometer is greater than or equal to 19,
         or less than or equal to 24, the green LED will turn on */

      potValue = analogRead(potPin); // Reads the value on the pin
      potValue = map(potValue, 0, 1023, 0, 31); // Changes the default range from 0 to 1023 to 0 to 31

      Serial.println(potValue, BIN);
      delay(500);

      digitalWrite(LED_RED, LOW);
      digitalWrite(LED_ORANGE, LOW);
      digitalWrite(LED_YELLOW, LOW);
      digitalWrite(LED_GREEN, HIGH);
      digitalWrite(LED_BLUE, LOW);
    }
    else if (potValue >= 25 && potValue <= 31) {
      /*If the value on the potentiometer is greater than or equal to 25,
        or less than or equal to 31, the blue LED will turn on */

      potValue = analogRead(potPin); // Reads the value on the pin
      potValue = map(potValue, 0, 1023, 0, 31); // Changes the default range from 0 to 1023 to 0 to 31

      Serial.println(potValue, BIN);
      delay(500);

      digitalWrite(LED_RED, LOW);
      digitalWrite(LED_ORANGE, LOW);
      digitalWrite(LED_YELLOW, LOW);
      digitalWrite(LED_GREEN, LOW);
      digitalWrite(LED_BLUE, HIGH);
    }
  } while (true);
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void blinkError() {

  /////// The 'error' flag ///////

  int brightness = 0;

  // The for loop will loop 5 times
  for (int x = 0; x < 5; x++) {

    digitalWrite(LED_RED, HIGH);
    delay(100);
    digitalWrite(LED_RED, LOW);
    delay(100);

    // Changes the brightness of the LED so that it is half bright
    brightness++;
    brightness %= 128;
    analogWrite(LED_RED, brightness);
  }
}

Answer 1

In your char dataInput() function you are taking the serial input with Serial.parseInt() which when inputting 'A' parseInt will return 0. See the documentation . In order to read a char use Serial.read() to get a single character.

void loop() {

  Serial.println ("Enter your chosen operator");
  Serial.println ("A for Addition, S for Subtraction, M for Multiplication,");
  Serial.println ("D for Division, and P for Potentiometer: ");

  // Takes an input from the user
  char theOperator = Serial.read();

  switch(theOperator) {
    case 'A':
    // If input is equal to 1, carry out function 'addition()'
      addition();
      break;
    case 'S':
    // If input is equal to 2, carry out function 'subtraction()'
      subtraction();
      break;
    case 'M':
    // If input is equal to 3, carry out function 'multiplication()'
      multiplication();
      break;
    case 'D':
    // If input is equal to 4, carry out function 'division()'
      division();
      break;
  case 'P':
    // If input is equal to 5, carry out function 'potentiometer()'
    potentiometer();
    break;
  }
}