View Compilation Error

0_0_37132197_11272.cpp: In function 'void build_tree(char*, int, int)':
0_0_37132197_11272.cpp:22:25: error: 'strlen' was not declared in this scope
     int len = strlen(str);
                         ^
0_0_37132197_11272.cpp: In function 'void solve(int, char*)':
0_0_37132197_11272.cpp:59:23: error: 'strlen' was not declared in this scope
     int len = strlen(s);
                       ^
0_0_37132197_11272.cpp: In function 'int main()':
0_0_37132197_11272.cpp:75:35: error: 'memset' was not declared in this scope
         memset(tree,0,sizeof(tree));
                                   ^