[Someone]

"If it's only a single line in after the if, the braces are optional."

Not _line_, _statement_. Consider

  if(flag)
    foo(); bar();

and

  if(flag)
    foo =
      bar +
      baz;

That first example always calls bar().

Warning: I haven't tested this, and am beginning to doubt a bit. It must be correct, but why, then, don't I remember seeing this in underhanded C contests? Combining that with macros allows you to hide the semicolon.