View Compilation Error

0_0_21299274_20470.cpp:3:5: error: 'stack' does not name a type
     stack<TreeNode*>sta;
     ^
0_0_21299274_20470.cpp:4:23: error: expected ')' before '*' token
     Solution(TreeNode *root) {
                       ^
0_0_21299274_20470.cpp:10:5: error: 'TreeNode' does not name a type
     TreeNode* next() {
     ^
0_0_21299274_20470.cpp:17:18: error: 'TreeNode' has not been declared
     void goAlong(TreeNode *temp){
                  ^
0_0_21299274_20470.cpp: In member function 'bool Solution::hasNext()':
0_0_21299274_20470.cpp:8:17: error: 'sta' was not declared in this scope
         return !sta.empty();
                 ^
0_0_21299274_20470.cpp: In member function 'void Solution::goAlong(int*)':
0_0_21299274_20470.cpp:19:13: error: 'sta' was not declared in this scope
             sta.push(temp);
             ^
0_0_21299274_20470.cpp:20:26: error: request for member 'left' in '* temp', which is of non-class type 'int'
             temp = temp->left;
                          ^