View Compilation Error

1_858_4007_9102.cpp: In function 'void init()':
1_858_4007_9102.cpp:7:38: error: 'memset' was not declared in this scope
 #define mst(a,b) memset(a,b, sizeof b)
                                      ^
1_858_4007_9102.cpp:33:2: note: in expansion of macro 'mst'
  mst(vis, 0);
  ^