refactor: Improve documentation and code quality

separate_codes/Export_EURUSD_History.mq5

@@ -9,28 +9,35 @@
 #property script_show_inputs
 
 //--- input parameters
-input string InpFileName = "raw_price_data.csv"; // File name
-input int    InpDays     = 1000;                 // Number of days
+input string InpFileName = "raw_price_data.csv"; // File name to save the data to
+input int    InpDays     = 1000;                 // Number of days of historical data to export
 
 //+------------------------------------------------------------------+
 //| Script program start function                                    |
 //+------------------------------------------------------------------+
 void OnStart()
   {
+//--- Array to store the price data
    MqlRates rates[];
+//--- Variable to store the number of bars copied
    int      copied;
 
-   //--- get daily price data
+//--- Get daily price data for EURUSD for the specified number of days
    copied = CopyRates("EURUSD", PERIOD_D1, 0, InpDays, rates);
+   
+//--- Check if the data was copied successfully
    if(copied > 0)
      {
+      //--- Open the file to write the data to
       int file_handle = FileOpen(InpFileName, FILE_WRITE | FILE_CSV | FILE_ANSI, ',');
+      
+      //--- Check if the file was opened successfully
       if(file_handle != INVALID_HANDLE)
         {
-         //--- write header
+         //--- Write the header row to the CSV file
          FileWrite(file_handle, "Time", "Open", "High", "Low", "Close", "Volume");
 
-         //--- write data
+         //--- Loop through the copied data and write each row to the CSV file
          for(int i = 0; i < copied; i++)
            {
             FileWrite(file_handle,
@@ -42,17 +49,20 @@ void OnStart()
                       rates[i].tick_volume);
            }
 
+         //--- Close the file
          FileClose(file_handle);
          Print("Data successfully exported to ", InpFileName);
         }
       else
         {
+         //--- Print an error message if the file could not be opened
          Print("Error opening file: ", GetLastError());
         }
      }
    else
      {
+      //--- Print an error message if the data could not be copied
       Print("Error copying rates: ", GetLastError());
      }
   }
-//+------------------------------------------------------------------+
+//+------------------------------------------------------------------+