Doctor Fortran in “Source Form Just Wants to be Free”

In the beginning, there was only one source form for FORTRAN (as it was then known) programs. Each statement was exactly 72 characters long – no more, no less. (See note below.) Columns 1-5 were for statement labels, whole line comments were indicated with a C in column 1, and column 6 was reserved for a continuation indicator. Blanks in the statement field, outside of quoted literals, were ignored. The standard didn’t (and still doesn’t) talk about how source programs are fed into a compiler, but on systems where there were “file types”, the types .for, .f and .ftn were usually recognized as being Fortran.

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