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Q How to write Multi line MACRO ???  

#define MUL_LINE_MACRO(x)    do{  x=123; } while (0)
 http://c-faq.com/cpp/multistmt.html

Dont put ; after Macro let user put it  MUL_LINE_MACRO(x);

This is required as 

if in code macro is used in if else  condition like;

if (cond )

    MUL_LINE_MACRO(x);

else

   some ;

and macro also has an  ";"  then complilation fails 

if (cond )

      do{  x=123; } while (0);

  ; // this will cause compilation failure

else

   some ;