View Compilation Error

0_0_21849333_2453.cpp: In function 'int main()':
0_0_21849333_2453.cpp:50:20: error: 'struct node' has no member named 'top'
       node an = an.top(), bn = sb.top();
                    ^
0_0_21849333_2453.cpp:51:10: error: 'struct node' has no member named 'pop'
       an.pop(), bn.pop();
          ^
0_0_21849333_2453.cpp:51:17: error: 'bn' was not declared in this scope
       an.pop(), bn.pop();
                 ^