Source : Free On-Line Dictionary of Computing

indent style
     
         The rules one uses to indent code in a readable
        fashion.  There are four major {C} indent styles, described
        below; all have the aim of making it easier for the reader to
        visually track the {scope} of control constructs.  The
        significant variable is the placement of "{" and "}" with
        respect to the statement(s) they enclose and to the guard or
        controlling statement ("if", "else", "for", "while", or "do")
        on the block, if any.
     
        "K&R style" - Named after Kernighan & Ritchie, because the
        examples in {K&R} are formatted this way.  Also called "kernel
        style" because the {Unix} {kernel} is written in it, and the
        "{One True Brace Style}" (abbreviation 1TBS) by its partisans.
        The basic indent shown here is eight spaces (or one tab) per
        level; four spaces are occasionally seen, but are much less
        common.
     
         if (cond) {
        	
         }
     
        "Allman style" - named after Eric Allman, a Berkeley hacker
        who wrote a lot of the {BSD} utilities in it (it is sometimes
        called "BSD style").  Resembles normal indent style in
        {Pascal} and {ALGOL}.  Basic indent per level shown here is
        eight spaces, but four spaces are just as common (especially
        in C++ code).
     
         if (cond)
         {
        	
         }
     
        "Whitesmiths style" - popularised by the examples that came
        with {Whitesmiths C}, an early commercial C compiler.  Basic
        indent per level shown here is eight spaces, but four spaces
        are occasionally seen.
     
         if (cond)
        	{
        	
        	}
     
        "GNU style" - Used throughout {GNU} {Emacs} and the {Free
        Software Foundation} code, and just about nowhere else.
        Indents are always four spaces per level, with "{" and "}"
        halfway between the outer and inner indent levels.
     
         if (cond)
          {
            
          }
     
        Surveys have shown the Allman and Whitesmiths styles to be the
        most common, with about equal shares.  K&R/1TBS used to be
        nearly universal, but is now much less common.  The opening
        brace tends to get lost against the right parenthesis of the
        guard part in an "if" or "while", which is a {Bad Thing}.
        Defenders of 1TBS argue that any putative gain in readability
        is less important than their style's relative economy with
        vertical space, which enables one to see more code on one's
        screen at once.  Doubtless these issues will continue to be
        the subject of {holy wars}.
     
        [{Jargon File}]
     
        (1995-07-24)