HP Fortran Programmer's Reference (September 2007)

Language elements
Source format of program file
Chapter 252
written in columns 1 to 72. The compiler treats a line containing only blank characters in
columns 1 to 72 as a comment line. In addition, a line is considered to be a comment when
there is an exclamation mark (!) in column 1 or in any column except column 6.
The following are HP extensions to the comment:
• A line with D or d in column 1 is by default treated as a comment. The +dlines option
causes the compiler to treat such lines as statements to be compiled. This extension to the
comment—called debugging lines—is useful for including PRINT statements that are to be
compiled during the debugging stage to display the program state.
• A line with a pound sign (#) character in column 1 is treated as a comment. This extension
allows compilation of source files that have been preprocessed with the C preprocessor
(cpp).
• HP Fortran allows tab formatting. That is, a tab character may be entered in the first
column of a line to skip past the statement label columns. If the character following the
tab character is a digit, this digit is assumed to be in column 6, the continuation indicator
column. Any other character following the tab character is assumed to be in column 7, the
start of a new statement. A tab character in any other column of a line is treated as a
space.