The basic layout of an F90 program where the modules and functions are internal is as follows
module1 module2 program name implicit none constant/variable declarations parameter declarations data declarations use module1 use module2 body of program contains function1 function2 end program name
The general structure of a module (called module_name in this example) is as follows
module module_name (parameters) local variable declarations contains body of function code end module module_name
The structure of a function is very similar, but doesn't use contains - just replace "module" with "function".
A first code
Putting it into Practice:
|Here is a trivial first code that includes some output. Using emacs, open a file called hello.f90, and put the following into this file. Then save and quit emacs.|
PROGRAM HELLO IMPLICIT NONE ! write out "Hello World" to your x-term PRINT *, "Hello World!" END PROGRAM HELLO
|Now you should compile this code. At the prompt, type|
ifort hello.f90 -o hello
Note: ifort is the Intel Fortran compiler. Another common Fortran compiler is called gfortran (from GNU).
The program should have compiled without error, and made an executable called hello. This executable is now ready to run. To run it, type at the prompt (and then hit return)
|On your x-term, you should see the output Hello, World!|
Notes on your first code
- The first line starts the program, and gives a name to this program - in this case the name is HELLO.
- The second line is important - it means that you have to declare each variable/constant explicitly. Neglecting to include this line can give you problems when it comes to debugging!
- Comment statements are very important in all code. In F90, comment statements are prefixed by an exclamation mark (!). Get into the habit of writing helpful comment statements in your code.
- Each statement line in F90 is confined to 132 characters in length. To continue a line, use an ampersand (&) at the end of the old line, with the new line appearing directly underneath. The exception is when splitting a string (as seen in the example above) where you also need to prefix the 2nd line with an ampersand.
- You can include several statements on one line. Each statement on the line must be separated by a semicolon (;)