View Compilation Error

0_0_36627624_5525.cpp: In function 'int main()':
0_0_36627624_5525.cpp:11:38: error: 'memset' was not declared in this scope
 #define mem(a,b) memset(a,b,sizeof(a))
                                      ^
0_0_36627624_5525.cpp:55:3: note: in expansion of macro 'mem'
   mem(C, 0);
   ^