View Compilation Error

0_0_26317918_16370.cpp: In function 'int main()':
0_0_26317918_16370.cpp:91:27: error: cannot convert 'std::string {aka std::basic_string<char>}' to 'const char*' for argument '1' to 'size_t strlen(const char*)'
         int len=strlen(str);
                           ^
0_0_26317918_16370.cpp:105:25: error: 'destroy' was not declared in this scope
             destroy(root);
                         ^