View Compilation Error

0_0_34221556_14365.cpp: In function 'void c1::init()':
0_0_34221556_14365.cpp:16:31: error: 'memset' was not declared in this scope
   memset(head, 0, sizeof(head));
                               ^
0_0_34221556_14365.cpp: In function 'void c2::init()':
0_0_34221556_14365.cpp:60:31: error: 'memset' was not declared in this scope
   memset(head, 0, sizeof(head));
                               ^
0_0_34221556_14365.cpp: In function 'std::pair<int, int> c2::bfs(int)':
0_0_34221556_14365.cpp:73:31: error: 'memset' was not declared in this scope
   memset(book, 0, sizeof(book));
                               ^