View Compilation Error

0_0_18188679_23542.cpp: In function 'int main(int, const char**)':
0_0_18188679_23542.cpp:56:13: error: 'used' was not declared in this scope
         mem(used, false);
             ^
0_0_18188679_23542.cpp:28:32: note: in definition of macro 'mem'
 #define   mem(x,v)      memset(x,v,sizeof(x))
                                ^