View Compilation Error

0_0_18027200_14991.cpp: In function 'void init()':
0_0_18027200_14991.cpp:26:29: error: 'memset' was not declared in this scope
  memset(head,-1,sizeof(head));
                             ^
0_0_18027200_14991.cpp: In function 'int main()':
0_0_18027200_14991.cpp:100:28: error: 'memset' was not declared in this scope
   memset(pre,-1,sizeof(pre));
                            ^