View Compilation Error

0_0_15073566_13063.cpp: In function 'void print()':
0_0_15073566_13063.cpp:32:21: error: 'class std::stack<char>' has no member named 'front'
   printf("%c\n",str.front());
                     ^
0_0_15073566_13063.cpp: In function 'int main()':
0_0_15073566_13063.cpp:40:7: error: 'class std::stack<char>' has no member named 'clear'
   str.clear();
       ^