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We can now perform operations on whole arrays and partial arrays (array sections) without having to refer to individual elements. This shortens program development time and greatly clarifies the meaning of programs.

Array constructors can be used to assign values to rank 1 arrays within a program unit. The RESHAPE function allows us to assign values to a two or higher rank array when used in conjunction with an array constructor.

We have introduced the concept of a deferred-shape array. Arrays do not need to have their shape specified at compile time, only their rank. Their actual shape is deferred until runtime. We achieve this by the combined use of the ALLOCATABLE attribute on the variable declaration and the ALLOCATE statement, which makes Fortran a very flexible language for array manipulation.

We now have the following concepts for the use of subroutines:

We now have a lot of the tools to start tackling problems in a structured and modular way, breaking problems down into manageable chunks and designing subprograms for each of the tasks.

We have now introduced the concept of a module, another type of program unit, probably one of of the most important features of Fortran 90. We have seen in this chapter how they can be used:

This is a very powerful addition to the language, especially when constructing large programs and procedure libraries.

This chapter has shown some of the options open to you when working with legacy code. The emphasis has been on relatively straightforward code restructuring. The use of software tools to aid in this is highly recommended as converting manually using an editor is obviously going to involve much more work.

In Chapter 26 we will look at an example that involves a major rewrite using user defined data types.

We can now perform operations on whole arrays and partial arrays (array sections) without having to refer to individual elements. This shortens program development time and greatly clarifies the meaning of programs.

Array constructors can be used to assign values to rank 1 arrays within a program unit. The RESHAPE function allows us to assign values to a two or higher rank array when used in conjunction with an array constructor.

We have introduced the concept of a deferred-shape array. Arrays do not need to have their shape specified at compile time, only their rank. Their actual shape is deferred until runtime. We achieve this by the combined use of the ALLOCATABLE attribute on the variable declaration and the ALLOCATE statement, which makes Fortran a very flexible language for array manipulation.

Support for the above is relatively limited at the time of writing this book. There is always a time lag between the formal publication of a standard and the implementation in production compilers. As compiler support improves examples will be added to our web site. Our home page is:

These features provide us with a safer way of addressing certain types of problems that would previously have had to be tackled using pointers.

There are no compilers at this time that fully support the above. We hope this has whetted your appetite for what will be possible in the future with Fortran 2003 conformant compilers.

The following are some practical rules and guidelines: