View Compilation Error

0_0_18339193_26850.cpp: In function 'void init()':
0_0_18339193_26850.cpp:16:32: error: 'memset' was not declared in this scope
  memset(ch[0], 0, sizeof(ch[0]));
                                ^
0_0_18339193_26850.cpp: In function 'void insert(int)':
0_0_18339193_26850.cpp:26:34: error: 'memset' was not declared in this scope
    memset(ch[u], 0, sizeof(ch[u]));
                                  ^