c - 我的搜索功能无法正常工作，因为我的 if 语句有问题，并且我正在使用链表

Question

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>

#define TRUE 1
#define FALSE 0

void new_contact();//add contact using linked list
void list_contact();
void delete_contact();

//int sorting_contact();//sort contact name using sorting
void search_contact();//search for contact phone number using searching

struct contact
{
    char phone_number[20];
    char contact_name[70];
    char address [80];
    struct contact *ptrnext;
};

struct contact *headptr, *newptr, *currentptr, *previousptr;

int main()
{
    system("color B");
    int key;
    char ch;
    int choice=TRUE;
    headptr=(struct contact *)NULL;

    while(choice==TRUE)
    {

        printf("\n\t\tWelcome to Smart Phone Book System");
        printf("\n\nAdd a contact :A\nList a contact :L\nDelete a contact :D"
               "\nSearch for contact :S\nSort phonebook :T\nExit :x\n");
        printf("\nPlease enter the mode you want:");
        scanf(" %c%*c", &ch);
        switch(ch)
        {
            case 'A': new_contact();system("CLS");break;

            case 'L': system("CLS");list_contact();break;

            case 'D': system("CLS");delete_contact();break;

            case 'S': search_contact();break;
            //case 'T': sorting_contact(); break;

            case 'X': choice=FALSE; break;

            default: system("CLS");printf("\nPlease enter a proper mode");
        }
    }
}

void new_contact()//add data
{
    newptr=(struct contact *)malloc(sizeof (struct contact)); // pointer to a new
                    //  memory allocation

    if (headptr==(struct contact *)NULL)//node is empty?
    {
         headptr=newptr; //first pointer point to first node
         newptr->ptrnext=(struct contact *)NULL; //first node pointer point to null
    }
    else
    {
         newptr->ptrnext=headptr;// new node pointer point to previous first node
         headptr=newptr; // head point to new node,new node become first node
    }
    printf("\nEnter a new name : ");
    fgets( newptr->contact_name,sizeof(newptr->contact_name),stdin);
    printf("\nEnter a number : ");
    fgets(newptr->phone_number,sizeof(newptr->phone_number),stdin);
    //scanf(" %d", &newptr->phone_number);
    //getchar();
    printf("\nEnter address : ");
    fgets(newptr->address,sizeof(newptr->address),stdin);
}

void list_contact()
{
    int i=1;
    if (headptr==(struct contact*)NULL) //empty list
    {
        printf("\nEmpty list");
        return;
    }

    currentptr=headptr;
    do
    {
        printf("\nContact  number %d",i);
        printf("\nName : %s", currentptr->contact_name);
        printf("\nPhone number : %s", currentptr->phone_number);
        printf("\n\nAddress : %s", currentptr->address);

        i++;
        printf("\n");
        currentptr=currentptr->ptrnext; //point to next node
    }

    while(currentptr !=(struct contact *)NULL);
}

void delete_contact()
{
    char contact_name_delete[20];

    if (headptr==(struct contact *)NULL)//node is empty?
    {
        printf("\n\nThe list is empty. Cannot delete!!!\n");
        //inform the user that the list is empty
    }
    else
    {
        printf("\nDelete list by name.");
        printf("\nEnter contact name to delete: ");
        fgets(contact_name_delete,sizeof(contact_name_delete),stdin);

        currentptr=headptr;

        while(currentptr ->ptrnext!=(struct contact *)NULL)
        {

            if (strncmp(currentptr->contact_name,contact_name_delete,6)==0) 
            //found the location
            {
                break;
            }
            else
            {
                previousptr=currentptr;//save the previous current address
                currentptr=currentptr->ptrnext; 
                //point to next node
            }
        }

        if (strncmp(currentptr->contact_name,contact_name_delete,6)==0)
        {
            if ( currentptr==headptr) //number is the first and only node in list
            {
                headptr=currentptr ->ptrnext; //head point to NULL
                free(currentptr);
            }
            else //delete at the middle of link list
            {
                previousptr->ptrnext=currentptr->ptrnext;
                free(currentptr);//destroy  node, free the memory.
            }
            printf("\nPhone number were deleted!\n");
        }
        else
            printf("\nNumber to be deleted is not in the list!!! ");
    }
}

我的问题出在 search_contact() 函数中:

void  search_contact()//The function for searching the contact based on name
{
    currentptr=headptr;
    char contact_name_add[30];
    if (headptr ==(struct contact *)NULL)
    {
        printf("The phonebook is empty..");
    }
    else
    {

        printf("Please enter the name of your contact for searching : ");//user inputs name for searching
        fgets(contact_name_add,sizeof(contact_name_add),stdin);//uses linear search concept

        printf("\n\nThe computer will now search for your contact");

        do
        {
            if (strncmp(currentptr->contact_name,contact_name_add,5)==0)
            {
                printf("\nName :         %s", currentptr->contact_name);
                printf("\nPhone Number : %s",currentptr->phone_number);
                printf("\nAddress :      %s", currentptr->address);
                currentptr=currentptr->ptrnext;
            }
            else
            {
                currentptr=currentptr->ptrnext;

我发现下面的行是我的问题，但我不知道为什么

                if (currentptr->ptrnext=NULL
                    && strncmp(currentptr->contact_name,contact_name_add,5)!=0)
                {
                    printf("\nThe name you seek is not in the phonebook~~");
                }
            }
        } while(currentptr!=(struct contact *)NULL);
    }
}

我可以很好地搜索我插入的联系人，但当我有 2 个或更多联系人时，就会出现问题。搜索功能与我的删除功能非常相似，但我将其编码为显示多于 1 个联系人(在联系人姓名相似的情况下)，但当它达到 NULL 时，它会给出错误，我找不到它在 Google 上(我在这方面做得不好)。

Answer 1

尝试使用以下 IF:

if(currentptr->ptrnext==NULL && strncmp(currentptr->contact_name,contact_name_add,5)!=0)