// Converting hex string to number in C++
// Demo for Oscar Oomens

const String hexDigits = "0123456789ABCDEF";

void setup() {
  String input = "1e00";

  Serial.begin(115200);

  long int result = 0;
  input.toUpperCase();
  for (int i = 0; i < input.length(); i++) {
    result <<= 4;
    result |= hexDigits.indexOf(input[i]);
  }

  Serial.println(result, HEX);
}

void loop() {
}