View Compilation Error

0_0_28371679_7574.cpp: In function 'int s1(int)':
0_0_28371679_7574.cpp:171:30: error: 'memset' was not declared in this scope
  memset(tree, 0, sizeof(tree));
                              ^
0_0_28371679_7574.cpp: In function 'int s2(int)':
0_0_28371679_7574.cpp:196:30: error: 'memset' was not declared in this scope
  memset(tree, 0, sizeof(tree));
                              ^