Fortran 90/95 Programming Manual

Fortran 90/95 Programming Manual1. Getting startedType, compile and run the following program (call the file hello.f90):program hello! this programs prints "hello world!" to the screenimplicit noneprint * , "Hello world!"end program helloNote the following:••••••a program starts with program program_nameit ends with end program program_nameprint * displays data (in this case, the character string “Hello, world!”) on thescreen.all characters after the exclamation mark (!) (except in a character string) areignored by the compiler. It is good programming practice to include comments.Comments can also start after a statement, for example:print * , “Hello world!” ! this line prints the message “Hello world!”Note the indentation. Indentation is essential to keep a program readable.Additionally, empty lines are allowed and can help to make the program readable.Fortran 90 allows both upper and lowercase letters (unlike FORTRAN 77, inwhich only uppercase was allowed).2. Types, Variables, Constants, OperatorsNames in Fortran 90A name or “identifier” in Fortran must adhere to fixed rules. They cannot be longer than31 characters, must be composed of alphanumeric characters (all the letters of thealphabet, and the digits 0 to 9) and underscores ( _ ), and the first character must be aletter. Identifiers are case-insensitive (except in character strings like “Hello world!” inthe example above); Thus, PRINT and print are completely identical.TypesA variable is a data object whose value can be defined and redefined (in contrast toconstants, see below). Variables and constants have a type, which can be one of the fiveintrinsic types, or a derived type. Intrinsic types are part of the Fortran language. Thereare five different intrinsic types. In Fortran 90, there is additionally the possibility ofdefining derived types, which are defined by the user (see below). The five intrinsictypes are:Integer TypeFor integer values (like 1, 2, 3, 0, -1, -2, …).4