AP_GPS: added comments in GPS_AUTO_test example sketch

Added comments in libraries/AP_GPS/examples/GPS_AUTO_text/GPS_AUTO_test.cpp file

AP_GPS: added comments to GPS_AUTO_test example sketch

Added comments in libraries/AP_GPS/examples/GPS_AUTO_text/GPS_AUTO_test.cpp file

AP_GPS: added comments to GPS_AUTO_test example sketch

AP_GPS: add comments to GPS_AUTO_text example sketch

AP_GPS: added comments in GPS_AUTO_test example sketch

libraries/AP_GPS/examples/GPS_AUTO_test/GPS_AUTO_test.cpp

@@ -16,7 +16,7 @@
      Test for AP_GPS_AUTO
 */
 
-#include <AP_HAL/AP_HAL.h>
+#include <AP_HAL/AP_HAL.h>                                      //This is a common Hardware Abstraction Layer.
 #include <AP_GPS/AP_GPS.h>
 #include <GCS_MAVLink/GCS_Dummy.h>
 #include <AP_Notify/AP_Notify.h>
@@ -24,10 +24,10 @@
 #include <AP_SerialManager/AP_SerialManager.h>
 #include <AP_BoardConfig/AP_BoardConfig.h>
 
-void setup();
-void loop();
+void setup();                                                   //This function is defined in most of the libraries. This function is called only once at boot up time. This function is called by main() function in HAL.
+void loop();                                                    //This function is defined in most of the libraries. This function is called by main function in HAL. The main work of the sketch is typically in this function only.
 
-const AP_HAL::HAL& hal = AP_HAL::get_HAL();
+const AP_HAL::HAL& hal = AP_HAL::get_HAL();                     //Declare "hal" reference variable. This variable is pointing to Ap_HAL::HAL class's object. Here, AP_HAL is library and HAL is a class in that library. This reference variable can be used to get access to hardware specific functions.                     
 
 static AP_BoardConfig board_config;
 
@@ -35,7 +35,7 @@ static AP_BoardConfig board_config;
 AP_BoardLED board_led;
 
 // create fake gcs object
-GCS_Dummy _gcs;
+GCS_Dummy _gcs;                                                 //gcs stands for Ground Control Station
 
 const AP_Param::GroupInfo GCS_MAVLINK_Parameters::var_info[] = {
         AP_GROUPEND
@@ -69,7 +69,7 @@ void print_latlon(AP_HAL::BetterStream *s, int32_t lat_or_lon);
 void print_latlon(AP_HAL::BetterStream *s, int32_t lat_or_lon)
 {
     int32_t dec_portion, frac_portion;
-    int32_t abs_lat_or_lon = labs(lat_or_lon);
+    int32_t abs_lat_or_lon = labs(lat_or_lon);                  //The labs() function in C++ returns the absolute value of a long or long int data.
 
     // extract decimal portion (special handling of negative numbers to ensure we round towards zero)
     dec_portion = abs_lat_or_lon / 10000000UL;
@@ -92,7 +92,7 @@ void loop()
     // Update GPS state based on possible bytes received from the module.
     gps.update();
 
-    // If new GPS data is received, output it's contents to the console
+    // If new GPS data is received, output its contents to the console
     // Here we rely on the time of the message in GPS class and the time of last message
     // saved in static variable last_msg_ms. When new message is received, the time
     // in GPS class will be updated.