View Compilation Error

0_0_35295662_23372.cpp: In constructor 'node::node()':
0_0_35295662_23372.cpp:19:35: error: 'memset' was not declared in this scope
         memset(nxt, 0, sizeof(nxt));
                                   ^
0_0_35295662_23372.cpp: In function 'node* find_node(char*)':
0_0_35295662_23372.cpp:55:25: error: 'strlen' was not declared in this scope
     int len = strlen(tel);
                         ^
0_0_35295662_23372.cpp: In function 'void getdata()':
0_0_35295662_23372.cpp:93:32: error: 'strcmp' was not declared in this scope
     while (strcmp(stime, "#end") != 0)
                                ^
0_0_35295662_23372.cpp: In function 'void calculate()':
0_0_35295662_23372.cpp:108:31: error: 'memset' was not declared in this scope
     memset(cnt, 0, sizeof(cnt));
                               ^