添加到链接列表的前面

Question

我能够成功地将名称添加到列表的末尾，但我无法将其添加到前面。 我想弄清楚如何添加到节点的前面，谢谢。 我以为我明白，要加到后面，你用最后一个屁股变量的代码将cout，所以我试图操纵，并使用头开始在开始。

#include <iostream> 
#include <string> 

using namespace std; 

struct node 
{ 
    string name; 
    string name1; 
    node *next; 

}; 

bool isEmpty(node *head); 
char menu(); 
void insert(node *&head, node *&last, string name); 
void insert_front(node *&head, node*&start, string name1); 
void insert_back(node *&head, node *&last, string name); 

void print(node *current); 
bool isEmpty(node *head) 
{ 
    if (head == NULL) 
     return true; 
    else 
     return false; 
} 


char menu() 
{ 
    char choice; 
    cout << "Menu\n"; 
    cout << "1. Add a name to the front of the list." << endl; 
    cout << "2. Add a name to the back of the list." << endl; 
    cout << "3. Print the list." << endl; 
    cout << "4. Exit." << endl; 
    cin >> choice; 
    return choice; 
} 

void insert(node *&head, node *&last, string name) 
{ 
    node *temp = new node; 
    temp->name = name; 
    temp->next = NULL; 
    head = temp; 
    last = temp; 
} 

void insert_back(node *&head, node *&last, string name) 
{ 
    if (isEmpty(head)) 
     insert(head, last, name); 
    else 
    { 
     node *temp = new node; 
     temp->name = name; 
     temp->next = NULL; 
     last->next = temp; 
     last = temp; 
    } 
} 

void insert_front(node *&head, node *& start, string name1) 
{ 
    node *temp = new node; 
    temp->name1 = name1; 
    temp->next = head; 
    head = temp; 
} 
void print(node *current) 
{ 
    if (isEmpty(current)) 
     cout << "The list is emtpy." << endl; 
    else 
    { 
     cout << "List of names: \n"; 
     while (current != NULL) 
     { 
      cout << current->name << endl; 
      current = current->next; 
     } 
    } 

} 

int main() 
{ 
    node *head = NULL; 
    node *last = NULL; 
    node *start = NULL; 
    char choice; 
    string name, name1; 
    do 
    { 
     choice = menu(); 
     switch (choice) 
     { 
     case '1': 
      cout << "Enter first name to the front of the list: " << endl; 
      cin >> name1; 
      insert_front(head, start, name1); 
      break; 
     case '2': 
      cout << "Enter first name to the end of the list:" << endl; 
      cin >> name; 
      insert_back(head, last, name); 
      break; 
     case '3': print(head); 
      break; 
     case '4': 
      return 0; 
      break; 
     } 
    } while (choice != 4); 

} 

Answer 1

你有很多不相干的“东西”混入代码插入列表头。你的insert_front显然没有错;如果有问题，最有可能在其他地方。

我会缩小代码的范围，使其他大多数问题都被删除。我还用ctor正确初始化一个节点，让这个顺序码的东西：

#include <iostream> 

class linked_list { 

    struct node { 
     int value; 
     node *next; 

     node(int value, node *next) : value(value), next(next) {} 

     friend std::ostream &operator<<(std::ostream &os, node const &n) { 
      return os << n.value; 
     } 
    } *head = nullptr; 

public: 

    void add_front(int i) { 
     head = new node(i, head); 
    } 

    friend std::ostream &operator<<(std::ostream &os, linked_list const &ll) { 
     for (node *n = ll.head; n != nullptr; n = n->next) 
      os << *n << ' '; 
     return os; 
    } 

}; 

int main() { 
    linked_list data; 

    data.add_front(1); 
    data.add_front(2); 
    data.add_front(5); 
    std::cout << data; 
} 

Answer 2

我已经斩了你的代码到一个最小工作集，请研究并改写必要。请注意列表，注意当你想改变在main中定义的头或尾值时，你必须传递本身是指针的变量的地址。

#include <iostream> 
#include <string> 

using namespace std; 

struct node { 
    string name; 
    node* next; 
}; 

char menu() { 
    char choice; 
    cout << "Menu\n"; 
    cout << "1. Add a name to the front of the list." << endl; 
    cout << "3. Print the list." << endl; 
    cout << "4. Exit." << endl; 
    cin >> choice; 
    return choice; 
} 

bool isEmpty(node* current) { 
    return current == NULL; 
} 

void insert_front(node** head, string name) { 
    node* temp = new node; 
    temp->name = name; 
    temp->next = *head; 
    *head = temp; 
} 

void print(node* root) { 
    if (isEmpty(root)) 
     cout << "The list is emtpy." << endl; 
    else { 
     cout << "List of names: \n"; 
     node* current = root; 
     while (current != NULL) { 
      cout << current->name << endl; 
      current = current->next; 
     } 
    } 
} 

int main() { 
    node* head = NULL; 
    node* last = NULL; 
    char choice; 
    string name; 

    do { 
     choice = menu(); 
     switch (choice) { 
     case '1': 
      cout << "Enter first name to the front of the list: " << endl; 
      cin >> name; 
      insert_front(&head, name); 
      break; 
     case '3': print(head); 
      break; 
     case '4': 
      return 0; 
      break; 
     } 
    } while (choice != 4); 
}