Arrays

Arrays can store a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Numbers(1)

Numbers(2)

Numbers(3)

Numbers(4)

…

Arrays can be one- dimensional (like vectors), two-dimensional (like matrices) and Fortran allows you to create up to 7-dimensional arrays.

Declaring Arrays

Arrays are declared with the dimension attribute.

For example, to declare a one-dimensional array named number, of real numbers containing 5 elements, you write,

real, dimension(5) :: numbers

The individual elements of arrays are referenced by specifying their subscripts. The first element of an array has a subscript of one. The array numbers contains five real variables –numbers(1), numbers(2), numbers(3), numbers(4), and numbers(5).

To create a 5 x 5 two-dimensional array of integers named matrix, you write −

integer, dimension (5,5) :: matrix  

You can also declare an array with some explicit lower bound, for example −

real, dimension(2:6) :: numbers
integer, dimension (-3:2,0:4) :: matrix  

Assigning Values

You can either assign values to individual members, like,

numbers(1) = 2.0

or, you can use a loop,

do i  =1,5
   numbers(i) = i * 2.0
end do

One-dimensional array elements can be directly assigned values using a short hand symbol, called array constructor, like,

numbers = (/1.5, 3.2,4.5,0.9,7.2 /)

please note that there are no spaces allowed between the brackets ‘( ‘and the back slash ‘/’