View Compilation Error

0_0_26028638_31732.cpp: In function 'int main()':
0_0_26028638_31732.cpp:647:37: error: cannot convert 'std::string {aka std::basic_string<char>}' to 'const char*' for argument '1' to 'int puts(const char*)'
         puts(mypow(2LL,n).tostring());
                                     ^