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From: ebh@hou4b.UUCP
Newsgroups: net.lang.c
Subject: spaces(n) macro
Message-ID: <1141@hou4b.UUCP>
Date: Wed, 12-Sep-84 10:30:59 EDT
Article-I.D.: hou4b.1141
Posted: Wed Sep 12 10:30:59 1984
Date-Received: Fri, 14-Sep-84 20:51:27 EDT
Organization: AT&T-ISL, Holmdel, NJ
Lines: 23

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from Waiming Mok:
#define spaces(n)   do {int i=(n);while (i--) putchar(' ');}while (0)

You don't need the do .. while construct,  just make a compound
statement: 
#define spaces(n) {int i=(n);while(i--) putchar(' ');}
Remember, anywhere <statement> can go, {<decl-list>; <statement> ...}
can go.  One problem can crop up:  what if i is used elsewhere in the
code?  Imagine what spaces(i) would do.  Therefore, it's wise to use
some name that you never use in regular coding, like _.  Also, make _ a
register variable to avoid the overhead of allocating more stack space,
and for the obvious speed and space advantages.  Thus the final version
looks like this:
#define spaces(n) {int _=(n);while(_--) putchar(' ');}
And yes, things like spaces(foo*2) do work.

-Ed Horch  {houxm,ihnp4,akgua}!hou4b!ebh

p.s.  On systems that support it,
#define spaces(n)  printf("%*s", (n), "");
works just as well.