anchor.diff:  
   REM compare the output to the expected output
   FC actual.txt expected.txt
  +
  +REM return to previous directory
  +popd
  
positive.code: @ECHO OFF
  
  REM create bin directory if it doesn't exist
  if not exist ..\bin mkdir ..\bin
  
negative.code: javac  ..\src\seedu\addressbook\Addressbook.java -d ..\bin
  IF ERRORLEVEL 1 (
      echo ********** BUILD FAILURE ********** 
      REM return to previous directory
      popd
      exit /b 1
  )
  REM no error here, errorlevel == 0
  