Why use do { } while (0) in macro definition? [duplicate]

Answer 1

A do{}while(0) allows you to break from the loop:

do{
   expr1;
   foo();
   if ( cond )
      break;
   expr2;
   goo(); 
} while (0);

It's the same as a simple block {...} except that you can break execution when you want with the break statement. You couldn't do that in a simple code block, unless you have multiple checks, which can get cumbersome. It still gets executed once, because of the condition while(0).