View Compilation Error

0_0_29931356_8137.cpp: In function 'int main()':
0_0_29931356_8137.cpp:41:13: error: 'a' was not declared in this scope
         mem(a, 0);
             ^
0_0_29931356_8137.cpp:9:26: note: in definition of macro 'mem'
 #define mem(a, b) memset(a, b, sizeof(a))
                          ^