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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