cmd : command prompt windows compile main.f90 (result :Hello World),output
--------------------------------------------------------------------------
peter.vlasschaert@gmail.com,13/07/2022

Compile ,Linking and Building.
------------------------------

--------------------------------------------------------------------------
info : https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html
learn : advanced skills to compile programs.(also gnu compiler)
--------------------------------------------------------------------------

1e) step : Type here to search : cmd , enter.
2e) step : c:\Users\computername>
3e) step : save file as > main.f90 some directory : c:\test
4e) step : go to directory
           a) c:\Users\computername>cd..
           enter
           result : c:\Users>
           b) c:\Users>cd..
           enter
           result : c:\>
           c) c:\>cd test
           enter
           result :c:\test>

check windows file is here : main.f90 , copy file here
5e) step : compile "maim.f90"
    c:\test>gfortran main.f90 -o helloworld
    enter
    ( no message,compile finshed)
    result : c:\test>
6e) step : run helloworld
    c:\test> helloworld
    enter
    result : Hello World
    
rem : gfortran   "compiler"
      main.f90   "source code = program"
      -o         "attribute,how to compile the program "
      helloworld "executable: helloworld.exe"
------------------------------------------------------------
only can excute : helloworld from . cmd prompt ,not general.
linking .library , need complex relation attributes
-----------------------------------------------------------