/in/foo.cc: In function 'int main()':
/in/foo.cc:13:2: error: 'cur' was not declared in this scope
  cur=1;
  ^~~
/in/foo.cc:16:4: error: 'st' was not declared in this scope
    st.push(cur++);
    ^~
/in/foo.cc:17:6: error: 'st' was not declared in this scope
   if(st.top()==a[i])
      ^~