FortranForm[expr] prints as a Fortran language version of expr.
Standard arithmetic functions and certain control structures are translated.
FortranForm acts as a "wrapper", which affects printing, but not evaluation.
The width of output lines must be set explicitly by giving the option PageWidth -> n for the relevant output stream.
SetOptions[$Output, PageWidth -> 72] uses a line width of 72 characters for standard Mathematica output.
No declarations are generated.
See The Mathematica Book: Section 1.11.8 and Section 2.8.1.
See also: CForm, Compile.