Re: Loops (was Re: do { quit; } else { })

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Michael S <already5chosen@yahoo.com> writes:

[...]

I suspect that 'while' loop is here in C because Dennis Ritchie wanted
'do .. while() ' and thought that if the keyword is here anyway than
why not reuse it?

>
According to K&R, all of the basic control structures in C -- if,
while, for, do, and switch (and listed in that order) -- were
provided in BCPL, though not using the same syntax as in C,.

K&R1 does say that.  K&R2 dropped that statement.

BCPL's equivalent of C's do/while did not reuse the WHILE keyword.

From K&R1 :

    C provides the fundamental flow-control constructions required
    for well-structured programs: statement grouping; decision
    making (if); looping with the termination test at the top
    (while, for), or at the bottom (do); and selecting one of a
    set of possible cases (switch). (All of these were provided
    in BCPL as well, though with somewhat different syntax; that
    language anticipated the vogue for "structured programming"
    by several years.)

Today being Star Wars Day, I'll say that this is true "from a certain
point of view".  The statement in K&R1 is accurate, but it could be
misinterpreted to imply that BCPL had an equivalent to the C-style
for loop.  The BCPL for-command had two forms:

    FOR N = expression1 TO expression2 BY constant-expression
        DO command

and

    FOR N = expression1 TO expression2 DO command

BCPL also had:

    WHILE expression DO command
    command REPEATWHILE expression // like C's do/while
    UNTIL expression DO command
    command REPEATUNTIL expression
    command REPEAT                 // an infinite loop

Of course you could write the equivalent of a C-style for loop
using other constructs.

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */