这个该怎么定义res

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

运行结果及报错内容

我的解答思路和尝试过的方法

我想要达到的结果

#include <iostream> 
#define MAXSIZE 30
using namespace std;
#include <stack>
#include <vector>
struct BTNode
{
    char data;
    BTNode *lchild,*rchild;
    BTNode (char d){
    data = d;
    lchild = rchild = NULL; 
    }
};
class BTree
{
    BTNode * r;
    public:
    BTree()    {r = NULL;}
    //1.
    bool CreateBTree(string str)
    {
        int i = 0;
        char flag ;
        stack <BTNode *> st;
        BTNode * p; 
        while (i < str.size())
        {
            switch(str[i])
            {
                case '(':flag = 'L';st.push(p);break;
                case ')':if(!st.empty()){st.pop();break;} else return false;
                case ',':flag = 'R';
                default:
                    p = new BTNode (str[i]);
                    if(r == NULL)
                    {
                        r = p;
                    }
                    else 
                    {
                        if(!st.empty())
                        {
                            if(flag == 'L')st.top() -> lchild = p;
                            else st.top() -> rchild = p;    
                        }
                        else return false;
                    }
                
            }
            i++;
        }// end while 
        //串结束后，栈应该为空 
        if(!st.empty()) return false;
        else return true;
        return true;
    }
    
    //2.
    void inorder(BTNode *b)
    {
        if(b != NULL)
        {
            inorder(b->lchild);
            cout<<b->data;
            inorder(b->rchild);
        }
    }
    void InOrder(BTree& bt)
    {
        inorder(bt.r);
    }
    
    //3.前序
    void porder(BTNode *b)
    {
        if(b != NULL)
        {
            cout<<b->data;
            porder(b->lchild);
            porder(b->rchild);
        }
     } 
     void Porder(BTree& bt)
     {
         porder(bt.r);
     }
    
    //4.后序
    void postorder(BTNode *b)
    {
      if(b != NULL)
      {
         postorder(b->lchild);
         postorder(b->rchild);
         cout<<b->data;
      }    
    } 
    void PostOrder(BTree& bt)
    {
        postorder(bt.r);
    }
     
    //5.深度
    int height(BTNode *b)
    {
       if(b != NULL)
       {
          return 1+max(height(b->lchild),height(b->rchild)) ; 
       }
       else return 0;    
    } 
    int Height(BTree& bt)
    {
        return height(bt.r);
     } 
    
    //6.统计二叉树的结点个数 。
    int NodeNumber(BTNode *d)
    {
        if(d != NULL)
        {
            return 1+NodeNumber(d->lchild)+NodeNumber(d->rchild);
        }
        else return 0;
    }
    
    //7.统计二叉树的叶结点个数。
    int leaf(BTNode *b)
    {
        if(b != NULL)
        {
            if(b->lchild == NULL&&b->rchild == NULL)
            {
                return 1;
            }
            else
            {
                return leaf(b->lchild)+leaf(b->rchild);
            }
        }
        else return 0;
    }
    
    //8.统计二叉树的度为1的结点个数。
    int nodecount(BTNode *b)
    {
      if(b == NULL) 
    {
      return 0;
    }
   if(b->lchild == NULL&&b->rchild != NULL||b->rchild == NULL&&b->lchild != NULL)
   {
    return 1+nodecount(b->lchild) + nodecount(b->rchild); 
   }
   return nodecount(b->lchild)+nodecount(b->rchild);
   } 
   int NodeCount(BTree& bt)
   {
        nodecount(bt.r);
   }
        
    //9.输出二叉树中从每个叶子结点到根结点的路径。243
    bool lujing(BTNode *b,char x,vector<char> path,vector<char>& res)
    {
        if(b == NULL) return false;
        path.push_back(b->data);
        if(b->data == x)
        {
            path.pop_back();
            res = path;
            return true;
        }
        if(lujing(b->lchild,x,path,res))
        return true;
        else
        return lujing(b->rchild,x,path,res);
    }
    void LuJing(BTree& bt,char x,vector<char>&res)
    {
        vector<char> path;
        lujing(bt.r,x,path,res);
    }
        
    //在树上找结点x 
    BTNode * findNode(BTNode * b ,char x)
    {
        if(b == NULL) return NULL;
        else if(b -> data == x) return b;
        else 
        {
            BTNode * p = findNode(b ->lchild , x);
            if(p != NULL ) return p;
            else return findNode(b -> rchild , x);
        }
        
    }
    //获取根指针 
    BTNode * getRoot()
    {
        return r;
    }
};
int main()
{
    BTree tree;
    string str;
    cin >> str;
    char path[MAXSIZE];
    //1
    if(tree.CreateBTree(str)) 
    cout << "创建成功" <<endl;
    else cout << "创建失败" << endl;
     
    char x; 
    cout<<"请输入要查找的结点名称："<<endl;
    cin >> x;
    BTNode * root = tree.getRoot();//定义root为tree树根的指针 
    BTNode *p =tree.findNode(root,x); //在tree上进行查找 
    if(p != NULL) cout <<" 找到了\n" << endl;//p空，没找到，否则找到了。 
    else cout << "没有找到\n" <<endl;
    //2
    cout<<"中序遍历结果为："<<endl;
    tree.InOrder(tree);
    cout<<endl;
    //3
    cout<<"前序遍历结果为："<<endl;
    tree.Porder(tree);
    cout<<endl;
    //4
    cout<<"后序遍历结果为："<<endl;
    tree.PostOrder(tree);
    cout<<endl;
    //5
    cout<<"该树的深度为："<<endl;
    cout<<tree.Height(tree);
    cout<<endl;
    //8
    cout<<"度为一的结点个数为："<<endl;
    cout<<tree.NodeCount(tree);
    //9
    cout<<"从每个叶子结点到根结点的路径为:"<<endl;
    tree.LuJing(tree,x,path,res);
    return 0;
}