View Compilation Error

0_0_29991002_31188.cpp: In function 'int main()':
0_0_29991002_31188.cpp:14:38: error: 'f' was not declared in this scope
   unsigned char *a=(unsigned char *)&f;
                                      ^
0_0_29991002_31188.cpp:16:9: error: 'p' was not declared in this scope
         p--;
         ^