And gcc points out why. Because it was allowed at one time (in C++) it was introduced into C. Then the C++ guys discovered that it was inconsistent with if() (where it was forbidden from day 1) and removed it. ANSI followed (much) later in C. MS wants to be 'helpful' and allows it. But I would want to know which i is used if the outer block has one too. I would think MS to try to combine the old and new behavior in some MS-unique style and make a mess of it.