16.1: Definition

Last updated
Save as PDF

Page ID: 54366

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

Before a derived data type can be used, it must be defined. The definition will establish which pieces of information will be grouped together. Each piece of information included in the definition is referred to as a component.

type type_name
    <component definitions>
end type type_name

For example, to declare the student type described previously, the following declaration would be appropriate:

type student
    character(50) :: name
    integer :: id
    real :: score
    character(2) :: grade
end type student

The indentation is not required, but does make the definition easier to read. The fields (name, id, score, grade) are called components. These components together make up the information for a 'student'.

The type definition is required only once at the beginning of the program. Once defined, the type definition cannot be changed. More specifically, additional components cannot be added unless the definition is updated and the program is recompiled.

This definition will establish a template as follows:

Once defined, the template can be used to declare variables. Each variable declared with this definition will be created based on the definition which includes these four components.