title: Arduino's string.toDouble() not working
body: <p>I am trying to convert a string to a double in one of my Arduino projects (specifically using a Teensy 3.5 in the Arduino IDE) using Arduino's <a href="https://www.arduino.cc/en/Reference/StringToDouble" rel="nofollow noreferrer"><code>string.toDouble()</code></a> command. When I try to implement the function as shown in the code below, I get the error:</p>
  
  <pre><code>&lt;'class String' has no member named 'toDouble'&gt;.
  </code></pre>
  
  <p>However, <code>string.toFloat()</code> and <code>string.toInt()</code> work successfully.</p>
  
  <p>Any ideas as to what is going wrong?</p>
  
  <pre class="lang-cpp prettyprint-override"><code>String myNumberString = "100";
  double myNumber = 0;
  
  void setup() {
    Serial.begin(9600);  
  }
  
  void loop() {
    myNumber = myNumberString.toDouble()+1;
    Serial.println(myNumber);
    myNumberString = String(myNumber);
    delay(1000);
  }
  </code></pre>