如何為鏈接列表C ++創建“ pop tail”功能

Question

晚上好！

我目前正在嘗試使用用於大學作業的單鏈接列表創建自定義堆棧。

我創建了一個工作彈出窗口，該彈出窗口刪除了mHead元素（列表的開頭），盡管我現在嘗試修改該函數以改為刪除mTail（列表中的最新節點）。 我創建了節點mPrev，以替換mNext的功能。 想法是將當前尾部設置為NULL，將新尾部設置為mPrev，這將是倒數第二個節點。 我相信每當我使用push（插入節點）時，都需要將mPrev設置為mHead的值。

Pop和Push是主要功能，大多數其他功能可以安全地忽略。

每當我按原樣運行代碼時，都會收到訪問沖突。 不言而喻，我對內容的現狀感到不滿意，因此，任何澄清或提示將不勝感激！

#include "stack.h"

Stack::Stack(){     //Constructor
   mHead = NULL;
   mTail = NULL;
   mPrev = NULL;
}

Stack::~Stack(){    //Deconstructor
}

/*
Function: int Stack::charConverter(char convertee)

*   Purpose : Convert char to numerical equivilent

*   Pre: A char to convert

*   Post : An integer is returned

****************************************************************/

int Stack::charConverter(char convertee){

   switch (convertee){

   case '1': return 1;
   case '2': return 2;
   case '3': return 3;
   case '4': return 4;
   case '5': return 5;
   case '6': return 6;
   case '7': return 7;
   case '8': return 8;
   default: return 9;

   }

}

/*
Function: bool Stack::checker(char searchKey)

*   Purpose : To determine whether a given character is a usable character (num or operator_

*   Pre: A character

*   Post : A bool is returned indicating whether or not the given is a usable character

****************************************************************/

bool Stack::checker(char searchKey){

   if ((searchKey == '1') || (searchKey == '2') || (searchKey == '3') || (searchKey == '4') || (searchKey == '5')
      || (searchKey == '6') || (searchKey == '7') || (searchKey == '8') || (searchKey == '9') || (searchKey == '+')
      || (searchKey == '-') || (searchKey == '*') || (searchKey == '/') || (searchKey == '^') || (searchKey == '=')){

      return true;

   }
   else {

      return false;

   }

}

/*
Function: void Stack::display()

*   Purpose : To display the entirety of the list

*   Pre: None (Though a populated list wouldn't hurt)

*   Post : The list is displayed

****************************************************************/

void Stack::display(){

   cout << "\n\nThe List: \n";

   Node *tmp = mHead;

   while (tmp != NULL){

      cout << tmp->mData;

      if (tmp->mNext != NULL)

         cout << "";

      tmp = tmp->mNext;

   }

   delete(tmp);

}

/*
Function: bool Stack::push(int data)

*   Purpose : To push a given character/number into the list

*   Pre: A character/number to add and a list to add to

*   Post : A new character/number is added

****************************************************************/

bool Stack::push(int data){

   Node *newNode;

   if (mHead == NULL){

      mHead = new Node(data);   //new case

      if (mHead == NULL)

         return false;

      mTail = mHead;    //add to end of case

   }

   else{

      if (isExist(data))
         return false;

      newNode = new Node(data);
      mTail->mNext = newNode;
      mTail = newNode;

      return true;

   }        //for else

   return true;

}   //either way, it is entered successfully

/*
Function: bool Stack::isExist(int searchKey)

*   Purpose : To determine whether a given character exists within the list

*   Pre: A populated list and character to search for

*   Post : A bool is returned indicating whether or not the given character exists

****************************************************************/

bool Stack::isExist(int searchKey){

   Node *tmp = mHead;

   while (tmp != NULL){

      if (tmp->mData == searchKey)
         return true;

      tmp = tmp->mNext;

   }

   return false;

}

/*
Function: bool Stack::isNumber(char searchKey)

*   Purpose : To determine whether a given character is a number

*   Pre: A character

*   Post : A bool is returned indicating whether or not the given is a number

****************************************************************/

bool Stack::isNumber(char searchKey){

   if ((searchKey == '1') || (searchKey == '2') || (searchKey == '3') || (searchKey == '4') || (searchKey == '5') 
      || (searchKey == '6') || (searchKey == '7') || (searchKey == '8') || (searchKey == '9')){

      return true;

   }
   else {

      return false;

   }

}

/*
Function: bool Stack::operate(int num1, int num2, char function)

*   Purpose : Perform mathematical functions

*   Pre: 2 numbers to operate on and an operator

*   Post : An integer is returned

****************************************************************/

int Stack::operate(int num1, int num2, char function){

   switch (function){

      case '*': return (num1*num2);
      case '-': return (num1-num2);
      case '+': return (num1+num2);
      case '^': return (num1^num2);
      case '/': return (num1/num2);

   }

}

/*
Function: char Stack::pop()

*   Purpose : To pop the top of the list

*   Pre: A list with at least 1 character

*   Post : The list has 1 less character

****************************************************************/

char Stack::pop(){

   Node *tmp;

   char data;       //when nothing to pop, it will return this value

   if (mTail != NULL){

      tmp = mTail;      //tmp pointing at node to be deleted

      if (mHead == mTail){

         mHead = NULL;
         mTail = NULL;

      }

      else{

         mTail = mTail->mPrev;

      }

      tmp->mPrev = NULL;
      data = tmp->mData;
      delete tmp;

   }

   return data;

}

/*
Function: char Stack::returnNumber(char searchKey)

*   Purpose : To recieve a char input and output the corresponding int

*   Pre: A char that has been checked using isNumber()

*   Post : An int is returned

****************************************************************/

int Stack::returnNumber(char searchKey){

   //Before using this function, be sure to make sure the input is a number using isNumber()

   switch (searchKey){

      case '1': return 1;
         break;
      case '2': return 2;
         break;
      case '3': return 3;
         break;
      case '4': return 4;
         break;
      case '5': return 5;
         break;
      case '6': return 6;
         break;
      case '7': return 7;
         break;
      case '8': return 8;
         break;
      default: return 9;

   }

}

/*
Function: int Stack::top()

*   Purpose : To return the value of the top member of the stack

*   Pre: A stack with node(s)

*   Post : An int is returned

****************************************************************/

int Stack::top(){  //Essentiall a get function  

   Node *tmp = mTail;

return tmp->mData;

}

void Stack::userInput(){

   bool validation = false;
   string userInput, junk;
   int lengthCheck = 1;

   while (validation == false){

      cout << "\nEnter your equation in postfix: ";
         getline(cin, userInput);

         for (char & input : userInput)     
         {

            if (((lengthCheck == 1) || (lengthCheck == 2)) && (isNumber(input) == 0)){    //Make sure first character is a number is a number
               cout << ERROR_INVALID_FIRST_LAST << endl;
               break;

            } else if (checker(input) == 0){
                  cout << ERROR_INVALID_INPUT;     //Make sure everything is a valid character
                  break;
            } else {
               push(input);
            }

            lengthCheck++;
         } 
   }

}





#ifndef _STACK_H
#define _STACK_H

#include <string>
#include <iostream>
#include <iomanip>
#include "header.h"

using namespace std;

const string ERROR_INVALID_INPUT = "\nError: The input you have entered is invalid, remember to use only operators and single digits. ";
const string ERROR_INVALID_FIRST_LAST = "\nError: First and last character must always be a number, and last a '='. ";

class Stack{

private:

   struct Node{
      int mData;
      Node *mNext, *mPrev;      //Node gives int and next pointer

      Node(){       //Default constructor
         mNext = NULL;
         mPrev = NULL;
      }

      Node(int value){
         mData = value;
         mNext = NULL;
      }
   };

   Node *mHead, *mTail, *mPrev;     //Start and end of list

public:

   Stack();

   ~Stack();

   int charConverter(char convertee);

   bool checker(char searchKey);

   void display();

   bool push(int data);

   bool isExist(int searchKey);

   bool isNumber(char searchKey);

   int operate(int num1, int num2, char function);

   char pop();

   int returnNumber(char searchKey);

   int top();

   void userInput();

};

#endif

Answer 1

您沒有將新創建的節點的mPrev分配給已經存在的尾節點。 因此，創建的節點沒有`mPrev'。 因此，在推功能中，添加以下內容：

  newNode = new Node(data);
  mTail->mNext = newNode;
  newNode -> mPrev = mTail;
  mTail = newNode;