菜單在C驅動程序鏈表

Question

下面的代碼工作正常，除了deleteEnd功能的所有功能進行各種操作。當我執行程序時，所有的函數都執行它們應該執行的任務，但是deleteEnd函數什麼也不做。鏈接列表在執行deleteEnd函數時沒有變化。請幫忙！！！！

#include<stdio.h> 
#include<conio.h> 
struct node{ 
    int data; 
    struct node *link; 
}*head = NULL, *new_node, *ptr=NULL, *prev_ptr, *temp; 

void insertBeg(){ 
    int info; 
    new_node = (struct node*)malloc(sizeof(struct node)); 
    printf("\nEnter data : "); 
    scanf("%d",&info); 
    new_node->data=info; 
    new_node->link=NULL; 
     if(head==NULL){ 
      head=new_node; 
     } 
     else{ 
      new_node->link=head; 
      head=new_node; 
     } 
} 

void insertEnd(){ 
    int info; 
    new_node = (struct node*)malloc(sizeof(struct node)); 
    printf("\nEnter data : "); 
    scanf("%d",&info); 
    new_node->data=info; 
    if(head==NULL){ 
     head=new_node; 
     new_node->link=NULL; 
    } 
    else{ 
     prev_ptr=head; 
     ptr=head->link; 
     while(ptr!=NULL){ 
      prev_ptr=ptr; 
      ptr=ptr->link; 
     } 
     prev_ptr->link=new_node; 
     new_node->link=NULL; 
    } 
} 

void displayNode(){ 
    printf("\nLinked List is : "); 
    ptr=head; 
    while(ptr!=NULL){ 
     printf("%d--->",ptr->data); 
     ptr=ptr->link; 
    } 
} 

void deleteBeg(){ 
    if(head==NULL){ 
     printf("\nUnderflow"); 
    } 
    else{ 
     temp=head; 
     head=head->link; 
     free(temp); 
    } 
} 

void deleteEnd(){ 
    if(head==NULL){ 
     printf("\nUnderflow"); 
    } 
    else{ 
     prev_ptr=head; 
     ptr=head->link; 
     while(ptr!=NULL){ 
      prev_ptr=ptr; 
      ptr=ptr->link; 
     } 
     prev_ptr->link=NULL; 
     free(ptr); 
    } 
} 

void traverse(){ 
    int count=0; 
    ptr=head; 
    while(ptr!=NULL){ 
     ptr=ptr->link; 
     count++; 
    } 
    printf("\nNumber of elements in the list are : %d",count); 
} 

void main(){ 
    int choice,ch='y'; 
    clrscr(); 
    label: 
    printf("\nPress 1 to insert at beg\n2 to insert at end"); 
    printf("\n3 to delete from beg\n4 to delete from end"); 
    printf("\n5 to display the list\n6 to traverse the linked list : "); 
    scanf("%d",&choice); 
    switch(choice){ 
     case 1: insertBeg(); 
      break; 
     case 2: insertEnd(); 
      break; 
     case 3: deleteBeg(); 
      break; 
     case 4: deleteEnd(); 
      break; 
     case 5: displayNode(); 
      break; 
     case 6: traverse(); 
      break; 
     default: printf("\nInvalid Option"); 
    } 
    printf("\nPress y to continue or any other key to exit : "); 
    scanf("%s",&ch); 
    if(ch=='y' || ch=='Y'){ 
     goto label; 
    } 
    getch(); 
} 

Answer 1

循環

while(ptr!=NULL){ 

運行，直到ptr是NULL，這意味着以後調用free(ptr)沒有影響。

您可以通過退出循環一次迭代更快，而不是

void deleteEnd(){ 
    if(head==NULL){ 
     printf("\nUnderflow"); 
    } 
    else{ 
     prev_ptr=head; 
     ptr=head; 
     while(ptr->link!=NULL){ 
      prev_ptr=ptr; 
      ptr=ptr->link; 
     } 
     prev_ptr->link=NULL; 
     free(ptr); 
    } 
} 

解決這個問題你可能要考慮採用特殊處理的情況下延長這一地方到底元素是head