View Compilation Error

0_0_37441206_23287.cpp:16:1: error: invalid use of template-name 'std::stack' without an argument list
 stack stk;
 ^
0_0_37441206_23287.cpp: In function 'int main()':
0_0_37441206_23287.cpp:49:4: error: 'stk' was not declared in this scope
    stk.push(x);
    ^
0_0_37441206_23287.cpp:66:10: error: 'stk' was not declared in this scope
   while(!stk.empty()){
          ^