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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 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 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.

Characters represent a different data type to any other in Fortran, and as a consequence there is a restricted range of operations which may be carried out on them.

A character variable has a length which must be assigned in a CHARACTER declaration statement.

Character strings are delimited by apostrophes (’) or quotation marks (“). Within a character string, the blank is a significant character.

Character strings may be joined together (concatenated) with the // operator.

Substrings occurring within character strings may be also be manipulated. There are a number of functions especially for use with characters:

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.

It is hoped that you now have some idea about the wide variety of uses that programming languages are put to.

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.

The following are some practical rules and guidelines:

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:

Another type of data — logical — is also recognised. A LOGICAL variable may take one of two values — or .