Diverse

C help

## String handling
https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/

Functions
    LANGUAGE charAt()
    LANGUAGE compareTo()
    LANGUAGE concat()
    LANGUAGE c_str()
    LANGUAGE endsWith()
    LANGUAGE equals()
    LANGUAGE equalsIgnoreCase()
    LANGUAGE getBytes()
    LANGUAGE indexOf()
    LANGUAGE lastIndexOf()
    LANGUAGE length()
    LANGUAGE remove()
    LANGUAGE replace()
    LANGUAGE reserve()
    LANGUAGE setCharAt()
    LANGUAGE startsWith()
    LANGUAGE substring()
        myString.substring(from)
        myString.substring(from, to)
    LANGUAGE toCharArray()
    LANGUAGE toDouble()
    LANGUAGE toInt()
    LANGUAGE toFloat()
    LANGUAGE toLowerCase()
    LANGUAGE toUpperCase()
    LANGUAGE trim()

Operators
    LANGUAGE [] (element access)
    LANGUAGE + (concatenation)
    LANGUAGE += (append)
    LANGUAGE == (comparison)
    LANGUAGE > (greater than)
    LANGUAGE >= (greater than or equal to)
    LANGUAGE < (less than)
    LANGUAGE <= (less than or equal to)
    LANGUAGE != (different from)

GPS distance

/**
  * A simple function that takes two GPS coordinates as input and outputs the distance between them in meter.
  * This example has been provided by chris from androidsnippets
  */
private double gps2m(float lat_a, float lng_a, float lat_b, float lng_b) {
  float pk = (float) (180/3.14169);

  float a1 = lat_a / pk;
  float a2 = lng_a / pk;
  float b1 = lat_b / pk;
  float b2 = lng_b / pk;

  float t1 = FloatMath.cos(a1)*FloatMath.cos(a2)*
     FloatMath.cos(b1)*FloatMath.cos(b2);
  float t2 = FloatMath.cos(a1)*FloatMath.sin(a2)*
     FloatMath.cos(b1)*FloatMath.sin(b2);
  float t3 = FloatMath.sin(a1)*FloatMath.sin(b1);
  double tt = Math.acos(t1 + t2 + t3);
 
  return 6366000*tt;
}

Random password

/*--------------------------------------------------------
 * Function: makePassword
 * Make a password with choosen length from a salt string
 * 
 * Parameters: 
 * lenght - Lenght of the password
 * 
 * Returns:
 * String containing a random password
 * 
 *------------------------------------------------------ */
function makePassword($lenght) {
	$salt = "abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ23456789";	// Salt to select chars from
	srand((double)microtime()*1000000); 					// Start the random generator
	$password=""; 								// Set the inital variable
	for ($i=0;$i<$lenght;$i++)  						// Loop and create password
		$password = $password . substr ($salt, rand() % strlen($salt), 1);
	return $password;
}