title: Fortran Undefined Reference Error
body: <p>I've installed gfortran through the MinGW-get installer.
  I'm facing issues when I call a subroutine in Fortran and try to compile.
  I have written a small program Hello.F and a subroutine World.F such that program Hello.F calls Subroutine World.F</p>
  
  <p>When I compile Hello.f using the command <code>gfortran Hello.F</code>
  I see an error as below,</p>
  
  <pre><code>Undefined Reference to 'World_'
  
  collect2.exe: error: Id returned 1 exit status
  </code></pre>
  
  <p>Below is Hello.F,</p>
  
  <pre><code>PROGRAM HELLO
  CALL WORLD
  STOP
  END
  </code></pre>
  
  <p>Below is World.F</p>
  
  <pre><code>SUBROUTINE WORLD
  print *, "Hello World!"
  RETURN
  END
  </code></pre>
  
  <p>Both programs Hello.F and World.F reside in the same folder and I <code>cd</code> to this folder before typing in the command <code>gfortran hello.f</code> to compile the program.</p>