View Compilation Error

0_0_35027721_22061.cpp: In function 'int Find(char, char*)':
0_0_35027721_22061.cpp:17:25: error: 'strlen' was not declared in this scope
  int i, len = strlen(str);
                         ^
0_0_35027721_22061.cpp: In function 'void trans(Bint&, char*)':
0_0_35027721_22061.cpp:42:32: error: 'memset' was not declared in this scope
  memset(a.num, 0, sizeof(a.num));
                                ^
0_0_35027721_22061.cpp:43:22: error: 'strlen' was not declared in this scope
  int len = strlen(str); //总长度
                      ^
0_0_35027721_22061.cpp: In function 'Bint mul(Bint, Bint)':
0_0_35027721_22061.cpp:61:32: error: 'memset' was not declared in this scope
  memset(m.num, 0, sizeof(m.num));
                                ^