链接列表程序错误

Question

在C中为链接列表编写了此程序。在尝试插入链表末尾时出现分段错误时，出现插入错误。其他所有情况都是在初始插入，插入2个元素之间等工作。花了很多时间思考，但无法弄清楚？

#include<stdio.h> 
#include<stdlib.h> 
#include<malloc.h> 

void insert(); 
void display(); 
void search(); 
void delete(); 
struct node{ 
    int val; 
    struct node *next; 
}*head; 
int num,count=0; 

void main() 
{ 
    char dec = 'E'; 
    printf("Welcome to the Linked List C Program!\n"); 
    head = NULL; 

    while(1){ 
     printf("Make a Choice:\n"); 
     printf("I.Insert\nD.Delete\nS.Search\nd.Display\nE.Exit\n"); 
     scanf(" %c",&dec); 
     switch(dec){ 
      case 'I': 
       insert(); 
       break; 
      case 'D': 
       delete(); 
       break; 
      case 'S': 
       search(); 
       break; 
      case 'd': 
       display(); 
       break; 
      case 'E': 
       exit(0); 
       break; 
      default: 
       printf("Wrong input Try Again!\n"); 
     } 
    } 
} 

void insert(){ 
    printf("Enter the number to insert:"); 
    scanf("%d",&num); 
    struct node *temp; 
    struct node *newnode; 
    struct node *prev; 
    int c =0; 
    //temp = (struct node *)malloc(sizeof(struct node)); 
    newnode = (struct node *)malloc(sizeof(struct node)); 
    //prev = (struct node *)malloc(sizeof(struct node)); 
    newnode->val = num; 
    if(head==NULL) 
    { 
     head = newnode; 
     head->next = NULL; 
    } 
    else 
    { 
     temp = head; 
     //searching whether linked list is in start or end 
     while(temp->val<num && temp !=NULL) 
     { 
      printf("Index:%d Value:%d Address:%p",c,temp->val,temp); 
      prev = temp; 
      temp = temp->next; 
      c++; 
      printf("TEST\n"); 

     } 
     if(c==0) 
     { 
      head = newnode; 
      head->next = temp; 

     } 
     else 
     { 
      prev->next=newnode; 
      newnode->next=temp; 
     } 
    } 
} 

void display() 
{ 
    struct node *temp; 
    temp = (struct node *)malloc(sizeof(struct node)); 
    temp = head; 
    while(temp != NULL) 
    { 
     printf("%d",temp->val); 
     temp = temp->next; 
    } 
    if(temp == NULL) 
    { 
     printf("Not present!"); 
    } 

} 

void search() 
{ 
    printf("Enter the number tosearch for:\n"); 
    scanf("%d",&num); 
    struct node *temp; 
    temp=head; 
    int c=0; 
    while(temp!=NULL) 
    { 
     if(temp->val==num) 
     { 
      printf("Present at position %d",c); 
      c++; 
     } 
     else if(temp == NULL) 
     { 
      printf("Not present!"); 
     } 
     else 
      c++; 
     temp =temp->next; 
    } 
} 

void delete() 
{ 
    struct node *temp; 
    struct node *prev; 
    temp = head; 
    printf("Enter the value to delete:\n"); 
    scanf("%d",&num); 
    int c=0; 
    while(temp!=NULL) 
    { 
     if(temp->val==num) 
     { 
      printf("Present at position %d",c); 
      printf("Deleting this element"); 
      prev->next=temp->next; 
      free(temp); 
      c++; 
     } 
     else 
      c++; 
     prev = temp; 
     temp =temp->next; 

    } 
    if(temp == NULL) 
    { 
     printf("Not present!"); 
    } 

} 

Answer 1

在while循环，你要检查temp的成员之一检查temp之前不为空：

while(temp->val<num && temp !=NULL) 

扭转：

while ((temp != NULL) && (temp->val < num))