// convert a hex string such as "A489B1" into an array like [0xA4, 0x89, 0xB1].

const byte MaxByteArraySize = 5;

const char aa[] = "\xE5";
const char ae[] = "\xE6";
const char oe[] = "\xF8";
const char a[] = "\x41";

int vals[] = {
  230, //  æ
  248, //  ø
  229, //  å
  198, //  Æ
  216, //  Ø
  197, //  Å
};

int val = 'a';

const char txt[] = "my string";
char *symbols[64] = {nullptr};

void setup() {
  Serial.begin(115200);

  for (int x : vals) {
    char c = (char)x;
    const char str[] = {(char)x, '\0'};
    Serial.print(x); Serial.print(" / "); Serial.print(x, HEX);
    Serial.print(" -> "); Serial.print(str);
    Serial.print(" / "); Serial.println(c);
  }
  delay(2000);
  
  int index = 0;
  symbols[index++] = aa;
  symbols[index++] = aa;
  symbols[index++] = ae;
  symbols[index++] = oe;
  symbols[index++] = a;
  symbols[index++] = oe;

  for (int i = 0; i<index; i++)
    Serial.print(i),
    Serial.print(" "),
    Serial.print(symbols[i]),
    Serial.print(" "),
    Serial.println(symbols[i], HEX);
  /*
  char *index, *ptr; 
  ptr = txt; Serial.print("ptr: '"); Serial.print(ptr); Serial.println("'"); delay(2000);
  int len = strlen(ptr);

  index = (ptr + (--len)); *index = '\0';
  Serial.print("ptr: '"); Serial.print(ptr); Serial.println("'"); delay(2000);
  */
}

void loop() {

}

/*
void setup()
{
  Serial.begin(115200);

  byte byteArray[MaxByteArraySize] = {0};

  hexCharacterStringToBytes(byteArray, "C3A5");
  dumpByteArray(byteArray, MaxByteArraySize);

  hexCharacterStringToBytes(byteArray, "A489B10");
  dumpByteArray(byteArray, MaxByteArraySize);
}


void hexCharacterStringToBytes(byte *byteArray, const char *hexString) {
  bool oddLength = strlen(hexString) & 1;
  byte currentByte = 0;
  byte byteIndex = 0;

  for (byte charIndex = 0; charIndex < strlen(hexString); charIndex++) {
    bool oddCharIndex = charIndex & 1;

    if (oddLength) {
      // If the length is odd
      if (oddCharIndex) {
        // odd characters go in high nibble
        currentByte = nibble(hexString[charIndex]) << 4;
      }
      else {
        // Even characters go into low nibble
        currentByte |= nibble(hexString[charIndex]);
        byteArray[byteIndex++] = currentByte;
        currentByte = 0;
      }
    }
    else {
      // If the length is even
      if (!oddCharIndex) {
        // Odd characters go into the high nibble
        currentByte = nibble(hexString[charIndex]) << 4;
      }
      else {
        // Odd characters go into low nibble
        currentByte |= nibble(hexString[charIndex]);
        byteArray[byteIndex++] = currentByte;
        currentByte = 0;
      }
    }
  }
}

void dumpByteArray(const byte * byteArray, const byte arraySize) {
  for (int i = 0; i < arraySize; i++) {
    Serial.print("0x");
    if (byteArray[i] < 0x10)
      Serial.print("0");
    Serial.print(byteArray[i], HEX);
    Serial.print(", ");
  }
  Serial.println();
}

byte nibble(char c) {
  if (c >= '0' && c <= '9')
    return c - '0';

  if (c >= 'a' && c <= 'f')
    return c - 'a' + 10;

  if (c >= 'A' && c <= 'F')
    return c - 'A' + 10;

  return 0;  // Not a valid hexadecimal character
}

void loop() {

  if( Serial.available()) {
    char buf[8];
    int n = Serial.readBytesUntil('\n', buf, sizeof(buf)-1); buf[n] = '\0';
    unsigned long hex = strtol(buf, 0, 10);
    Serial.print("buf: "); Serial.println(buf);
    Serial.print("hex: "); Serial.println(hex);
  }

  //byte byteArray[MaxByteArraySize] = {0};
  //hexCharacterStringToBytes(byteArray, "C3A5");
  //dumpByteArray(byteArray, MaxByteArraySize);
}
*/
/*
unsigned char rxBuf[2]= { 0xC3, 0xA5 };
char ReceString[32];

void setup() {
  Serial.begin( 9600);
  sprintf(ReceString, "\\\\x%02X%02X", (unsigned int)rxBuf[0], (unsigned int)rxBuf[1]);
  Serial.println(ReceString);
}

void loop() {
  if( Serial.available()) {
    Serial.print( "You have entered: ");
    delay(100);      // allow the rest of the line to be received.
    while( Serial.available()) {
      byte c = Serial.read();
      if( c != '\r' && c != '\n') {
        if( c <= 0x0F)
          Serial.print( "0");
        Serial.print( c, HEX);
        Serial.print( ", ");
      }
    }
    Serial.println();
  }
  delay(1);
}
*/

/*
unsigned char rxBuf[8]= { 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF, 0x11, 0x22 };
unsigned long rxId = 0x103;
char ReceString[32];

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

void loop() 
{
  sprintf(ReceString, "%03lX %02X%02X%02X%02X%02X%02X%02X%02XX", 
    rxId,
    (unsigned int) rxBuf[0],
    (unsigned int) rxBuf[1],
    (unsigned int) rxBuf[2],
    (unsigned int) rxBuf[3],
    (unsigned int) rxBuf[4],
    (unsigned int) rxBuf[5],
    (unsigned int) rxBuf[6],
    (unsigned int) rxBuf[7]);
  ReceString[3]=7+'0';
  Serial.println(ReceString);
  Serial.println(rxBuf[0]);
  delay(1000); 
}
*/