Re: IBM Acquires Rational Ada

[Hyman Rosen <hyrosen@mail.com>]

John R. Strohm wrote:

> Sorry.  That is a popular misconception.
>
> C was intended to be a high-level assembler for the PDP-11, that would be
> easy to translate into concise machine code.  That is where the ++ and --
> operators originally came from.  Specifically, Kernighan and Ritchie wanted
> to be able to use the indirect predecrement and indirect postincrement
> addressing modes of the PDP-11, which C expresses as *--var and *var++, so
> they hardwired them into the language.


No. According to Ritchie, in <http://cm.bell-labs.com/cm/cs/who/dmr/chist.html>:

     Thompson went a step further by inventing the ++ and -- operators,
     which increment or decrement; their prefix or postfix position
     determines whether the alteration occurs before or after noting
     the value of the operand. They were not in the earliest versions
     of B, but appeared along the way. People often guess that they were
     created to use the auto-increment and auto-decrement address modes
     provided by the DEC PDP-11 on which C and Unix first became popular.
     This is historically impossible, since there was no PDP-11 when B
     was developed. The PDP-7, however, did have a few `auto-increment'
     memory cells, with the property that an indirect memory reference
     through them incremented the cell. This feature probably suggested
     such operators to Thompson; the generalization to make them both
     prefix and postfix was his own. Indeed, the auto-increment cells
     were not used directly in implementation of the operators, and a
     stronger motivation for the innovation was probably his observation
     that the translation of ++x was smaller than that of x=x+1.