链表不能展示结果，

//films2.c   使用结构链表
#include <stdio.h>
#include <stdlib.h>    //提供malloc()原型
#include <string.h>    //提供strcpy()原型
#define TSIZE 45       //存放片名的数组大小
struct film{
    char title[TSIZE];
    int rating;
    struct film * next;    //指向链表的下一个结构
};

int main(void)
{
    struct film * head = NULL;    //初始化头指针
    struct film * prev, * current;
    char input[TSIZE];
    //收集并存储信息
    puts("Enter first movie title: ");
    while(gets(input) != NULL && input[0] != '\0')
    {
        current = (struct film *) malloc(sizeof(struct film));
        if (head = NULL)   //第一个结构
            head = current;
        else               //后续结构
            prev->next = current;
        current->next = NULL;
        strcpy(current->title,input);
        puts("Enter your rating <0-10>: ");
        scanf("%d",&current->rating);
        while(getchar() != '\n')
            continue;
        puts("Enter next movie title (empty line to stop): ");
        prev = current;    
    }
    //给出电影列表
    if(head = NULL)
        printf("No data entered. ");
    else
        printf("Here is the movie list: \n");
    current = head;
    while(current != NULL)
    {
        printf("Movie: %s Rating: %d\n",current->title,current->rating);
        current = current->next;
    }
    //任务已完成，因此释放所分配的内存
    current = head;
    while(current != NULL)
    {
        free(current);
        current = current->next;
    }
    printf("Bye!\n");
    return 0;
}

if(head = NULL)