//Student name: Ip Wing Yi
//Class: EG524403-1A
//Student number:230317896
//following is part 1
char buf[100] = {0};  // this is an array, total 100 nos. 
char inChar;
bool stringComplete = false;//two situation:true or fales
int i = 0;
//following is part 2
// declare/announce the function
char ConvertString(char);//will have this function in use
//following is part 3
void setup()
{
  // Initialize serial and wait for port to open
  Serial.begin(115200);
  while (!Serial)
  {
    // Wait for serial port to connect, needed for native USB port only
  }
}

void loop()//row 25-41 is a loop
{
  while (Serial.available())
  {
    inChar = (char)Serial.read(); // while loop's 1st step

    if (inChar == '\n')   // change '\n' to '~' when using Tinkercad
    {
      buf[i++] = inChar;  // last character is newline
      buf[i] = 0;         // string array should be terminated with a zero
      stringComplete = true;//as stringcomplete==true,will go row 43
    }
    else
    {
      // some actions after received
      inChar = ConvertString(inChar);
      buf[i++] = inChar;
    }
  }

  if (stringComplete)// only when received /n (enter), stringcomplete=true
  {
    Serial.print(buf);    // the printing of string will be stopped when zero is reached
    stringComplete = false;//when print
    i = 0;
  }
}

// body of the function
char ConvertString(char x)
{
  if (isUpperCase(x))
    return (toLowerCase(x));
  else if (isLowerCase(x))
    return (toUpperCase(x));
  else
    return (x);
}