View Compilation Error

0_0_18019077_1396.cpp: In function 'void buildgraph(int)':
0_0_18019077_1396.cpp:13:22: error: 'memset' was not declared in this scope
  memset(c,0,sizeof(c));
                      ^
0_0_18019077_1396.cpp: In function 'int ek(int, int)':
0_0_18019077_1396.cpp:29:28: error: 'memset' was not declared in this scope
   memset(pre,-1,sizeof(pre));        //璁板綍鐖惰妭鐐�
                            ^
0_0_18019077_1396.cpp: In function 'int main()':
0_0_18019077_1396.cpp:60:28: error: 'memset' was not declared in this scope
  memset(edge,0,sizeof(edge));
                            ^