Example: Hello World Programmes

• A first Fortran 90 programme. Notice that Fortran 90 is nearly free-format. Most modern programming languages separate statements with ";". in contrast Fortran 90 joins lines with "&".
  
  
• This second programme introduces SUBROUTINEs. The INTERFACE is implicit --- this is bad!
  
  
• Finally, a modern Fortran version with a MODULE --- the SUBROUTINE INTERFACE is explicit --- arguments are checked by the compiler.