Fortran 90/95 Programming Manual

Download Fortran 90/95 Programming Manual, free training course under 67 pages by Tanja van Mourik.

Table of contents

• Chapter 1 Getting started
• Chapter 2 Types, Variables, Constants, Operators
• Chapter 3 Control Constructs
• Chapter 4 Procedures
• Chapter 5 More on Arrays
• Chapter 6 Modules
• Chapter 7 More on I/O
• Chapter 8 Pointers
• Chapter 9 Numeric Precision
• Chapter 10 Scope and Lifetime of Variables
• Chapter 11 Debugging

Fortran 90 : Internal procedures

The three types of programs and subroutines can contain the CONTAINS statement. This statement separates the last executable statement from the program and marks the beginning of a collection of subroutines (subroutines or functions), called internal procedures. Unlike external routines, that is, those that are not located within a program or subroutine, these subroutines can only be used within the program that contains them. . In addition, these internal procedures have access to all the variables of the program that contains them (the host program), unless they include declarations of identifiers that bear the names of identifiers used in the host program.

These internal procedures allow on one side a better structuring of the tasks to be performed; on the other hand, sharing variables can be dangerous, since there is no way to prevent internal subroutines from modifying the contents of variables in the main program.

Variable declarations

An identifier allows to give a name to:

• a variable,
• a constant,
• a subroutine (subroutine or function).

An identifier must meet the following requirements:

• it is defined by a sequence of alphanumeric characters (non-accented letters, numbers, underscore),
• his first character must be a letter,
• its length is limited to 31 characters,
• we do not distinguish between uppercase and lowercase letters.

As a result: neither blanks nor special characters in the identifiers.