Beginner Fortran 90 tutorial

Download Free course and training document about Fortran 90, tutorial on 20 pages for beginners by Guy Munhoven.

Table of contents

• Basic program structure in Fortran
• Exercise
• Outputting data
• Reading data
• Do loops
• Functions
• Arrays
• Subroutines

General structure of a Fortran 90 program

Fortran 90 distinguishes the following program units (scoping units):

• main program;
• subroutines: subroutines and functions;
• modules;
• block data.

At first, we will not deal with modules or block data. It should be noted that the modules are among the most useful innovations of Fortran 90.

Main program

The main program has the following structure:

[PROGRAM [program name]]
specification and declaration instructions
executable instructions
[CONTAINS internal procedures]
END [PROGRAM [program name]]

Everything enclosed in square brackets ([...]) is optional (the brackets themselves are to be omitted in all cases). The PROGRAM statement is not mandatory, but the END statement. The latter can be completed by the PROGRAM attribute which must then be followed by the name of the program

name of the program. Different types of content (specification instructions
and declaration, executable instructions, etc.) are described below.

Subroutines

The subroutine subroutines have a structure similar to that of the main program:

SUBROUTINE name of the subroutine [(arguments)]
specification and declaration instructions
executable instructions
[CONTAINS internal procedures]
END [SUBROUTINE name of the subroutine]

The END statement is mandatory, but not the SUBROUTINE additional specification. If it is given, which is recommended, especially in the case where several subroutines are gathered in the same file, it must be
completed by the name of the subroutine, exactly as specified on the SUBROUTIN line.
Subroutines are run using the CALL command name of the subroutine [(arguments)]

functions

Function type subroutines return a result by calling them by name:

[type] FUNCTION function name ([argument list])
specification and declaration instructions
executable instructions
[CONTAINS internal procedures]
END [FUNCTION function name]

The type (see below) can be specified (recommended); otherwise, it is determined by the default typing rules (see below).