View Compilation Error

0_0_32779745_12499.cpp:25:1: error: 'stack' does not name a type
 stack<int,vector<int> > stk;
 ^
0_0_32779745_12499.cpp: In function 'void tarjan(int)':
0_0_32779745_12499.cpp:29:2: error: 'stk' was not declared in this scope
  stk.push(x);
  ^
0_0_32779745_12499.cpp:36:8: error: 'col' was not declared in this scope
    if(!col[*it]){
        ^
0_0_32779745_12499.cpp:48:4: error: 'pos' was not declared in this scope
    pos[x]=
    ^
0_0_32779745_12499.cpp:49:3: error: expected primary-expression before '}' token
   }
   ^