View Compilation Error

0_0_34105242_31725.cpp: In function 'int main()':
0_0_34105242_31725.cpp:44:24: error: cannot pass objects of non-trivially-copyable type 'std::string {aka class std::basic_string<char>}' through '...'
   while (scanf("%s",opr), opr[0] != 'E') {
                        ^