Fortran 90: Look and Feel

Source Format

There are now two types of formats: fixed form and free form.

Fixed form is the Fortran 77 standard plus

comments can start anywhere, and begin with an exclamation point "!"
multiple commands can be on one line, separated by a semicolon

Free form allows

comments can start anywhere, and must begin with an exclamation point "!"
multiple commands can be on one line, separated by a semicolon
line lengths up to 132 characters
continuation lines are signalled by an ampersand "&" at the end of the line being continued.

The current f77 convention of putting a "c" or "*" in column 1 for comments will generate a syntax error in free format form. The IBM compiler assumes free format unless the flag -q fixed is used. Existing f77 routines should be compiled with this flag.

Variable declarations

Variables can be declared according to the old syntax,

integer i,j
real*8 a(3,2)
integer imax
parameter (imax=30)

or a new syntax where the type can be followed by attributes. These are separated from the variable by a double colon. For example

integer :: i
real*8 :: a(3,2)
real*8, dimension(3,2) :: a
integer, parameter :: imax = 30
integer, allocatable :: b(:)

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