double  StringToDouble(
   string  value      // string
   );

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
//--- string to convert
   string str = "12345.54321";
//--- convert the input string as a real number into a double type variable
   double converted=StringToDouble(str);
//--- display the resulting number accurate to 8 decimal places in the journal
   PrintFormat("The string '%s' is converted to the real number %.8f", str, converted);
   /*
   result:
   The string '12345.54321' is converted to the real number 12345.54321000
   */
  }