View Compilation Error

0_0_28849207_11119.cpp: In function 'void solve()':
0_0_28849207_11119.cpp:45:26: error: 'memset' was not declared in this scope
  memset(dfn,0,sizeof(dfn));
                          ^
0_0_28849207_11119.cpp: In function 'int main()':
0_0_28849207_11119.cpp:77:30: error: 'memset' was not declared in this scope
   memset(head,-1,sizeof(head));
                              ^