New features

Fortran 90 provides several categories of arrays: explicit-shape (including automatic and adjustable), assumed-shape, deferred-shape (including allocatable and pointer), and assumed-size. They are each described later in this chapter.

Expressions may contain array operands and be array-valued. They may also contain array sections, which are array-valued. Function results may also be array valued. There is no implied order in which the element-by-element operations are performed. If such operations appear in an assignment statement where the left-hand side is an array, the effect is as if the right-hand side were completely evaluated before any part of the assignment takes place. A scalar may also be used in array expressions; more details of array expressions appear later in this chapter.

Certain array elements, selected by a mask, can be assigned in array assignment statements using the WHERE statement or WHERE construct. For any elemental operation in the assignments, only the elements selected by the mask participate in the computation.

Masked array assignments are described later in Chapter 5 and under the WHERE statement in Chapter 10.

A number of new intrinsic functions have been provided to manipulate arrays. They are mostly classed as transformational functions; see Chapter 11 for details.

A selected portion of an array, called an array section, can be specified. It is then treated as an array in its own right and can be used as such. The section can be specified by the use of subscript triplets, vector subscripts, or both.

It is possible to attach a substring specifier to the subscript list of a character array; the result is considered to be an array section, that (as noted above) is itself an array.

An array constructor allows an array to be constructed from a list of scalar values and arrays of any rank. An array constructor is a one-dimensional array and can be used wherever such an array is valid. Arrays of higher rank can be constructed by combining an array constructor with the RESHAPE intrinsic function.

Fortran 90 has introduced the concept of an array with no elements. These arrays are known as zero-sized arrays and allow certain algorithms to be written naturally without having to allow for edge conditions; more details are given later in this chapter.