Open Watcom FORTRAN 77 Language Reference

4 Arrays
4.1 Introduction
An array is a non-empty collection of data. Arrays allow a convenient way of manipulating large quantities
of data. An array can be referenced as an entity. In this way it is possible to conveniently pass large
quantities of data between subprograms. Alternatively, it is possible to reference each element of an array
individually so that data can be selectively processed. Consider the task of managing the marks of 100
students. Without arrays one would have to have a unique name for each mark. They might be M1, M2,
etc. up to M100. This is clearly cumbersome. Instead, we can use an array called MARKS containing 100
elements. Now there is one name for all the marks. Each mark can be referenced by using that name
followed by a subscript. Furthermore, suppose the size of the class doubled. Do we add the names M101,
M102, etc. up to M200? Not if we use arrays. If the size of the class doubled, all that need be done is to
define the array to contain 200 elements. It is not hard to see that programs that use arrays tend to be
general in nature. Arrays also facilitate the repetitive computations that must be performed on large
amounts of data in that they lend themselves to loop processing.
4.2 Properties of Arrays
Arrays are defined by an array declarator. The form of an array declarator is:
a( d [,d] ... )
where:
a
d
is the symbolic name of the array
is a dimension declarator.
The number of dimensions of the array is determined by the number of dimension declarators appearing in
the array declarator. Allowable dimensions for arrays range from 1 to 7. A 1-dimensional array can be
viewed as a vector, a 2-dimensional array as a matrix and a 3-dimensional array as a number of parallel
matrices. Arrays with dimension higher than 3 are generally difficult to intuitively describe and hence
examples will deal with arrays whose dimension is 1, 2 or 3.
Each dimension has a range of values. When referencing elements in that dimension, the dimension
expression must fall in that range. The range of a dimension is defined in the dimension declarator. A
dimension declarator has the following form:
Properties of Arrays 159