[英]Issue when comparing a value in a linked list in C
我正在用C语言编写一个“简单”程序,我们在其中创建一个链表,该链表的结构类似于电影,用于存储影片,标题,制作年份,评分(1-5)和指向该影片的指针。下一个节点。 我们不允许在此结构中添加任何内容或定义函数。
最重要的是,(出于某种原因)我们需要在main()的主体中编写整个链接列表,以便为该问题添加一定程度的意大利面条。 无论如何,在此程序中,我们应该让用户输入“ U”进行更新,或者输入“ S”进行电影搜索。 更新完成您所期望的,然后输入标题,年份,等级。 由此,我们应该将节点插入到链表的末尾 。
我们的搜索应循环访问此链接列表,如果找到匹配项,则应打印出电影,标题和年份。
尽管代码的更新部分有效,但似乎无法使搜索生效。 我正在使用一个名为temp的电影结构,该结构从头开始并遍历列表以尝试查找电影。 在通过printf运行了一些测试之后,我发现temp不管是什么,无论我输入什么电影,都只是一个空节点。
我假设这与我调用malloc的方式有关? 还是与未正确分配节点有关? 老实说,我不确定,很遗憾,实验室的TA也不知道D怎么了。
这是我的代码:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct movie_node {
char title[250];
int year;
unsigned char rating;
struct movie_node *next;
};
typedef struct movie_node movie;
int main() {
// variables
int loop = 1;
movie *head = NULL; // represents first
movie *current; // represents the last node
movie *temp; // used for traversing the linked list
head = malloc(sizeof(movie));
int amountOfMovies = 0; // increment after each addition
char choice; // either 'u' (update) or 's' (search)
// ask user for input
while(loop) {
printf("%d Movie(s) in the database. Update or search (U/S): ", amountOfMovies);
scanf(" %c", &choice);
/* CHOICE 1, UPDATE */
if(choice == 'U') {
// case 1, head is null, we must create a new node
if(head == NULL) {
// get input
printf("Name of the movie: ");
scanf(" %[^\n]%*c", head->title);
printf("Year: ");
scanf("%d", &head->year);
printf("Rating: ");
scanf("%hhu", &head->rating);
head->next = NULL;
head = current; // set head to point to current
} else {
current = head;
// need to find where current is
while(current != NULL) {
current = current->next;
} // end while
// current is now at the null position, indicating empty node
current = malloc(sizeof(movie)); // allocate mem
// get user input
printf("Name of the movie: ");
scanf(" %[^\n]%*c", current->title);
printf("Year: ");
scanf("%d", ¤t->year);
printf("Rating: ");
scanf("%hhu", ¤t->rating);
current->next = NULL;
} // end else
// output movie
printf("Movie \"%s\" is added to the database.\n", current->title);
amountOfMovies++; // increment amount of movies in database
} else if(choice == 'S') {
/* CHOICE 2, SEARCH */
// temp string
char tempTitle[250];
// flag to let us know if we found something
bool found = false;
// temp linked list to traverse
temp = head;
temp = malloc(sizeof(movie));
// ask user for input
printf("Name of movie: ");
scanf(" %[^\n]%*c", tempTitle);
printf("NAME OF MOVIE IN HEAD: %s\n", temp->title); // test, take out later
while(temp != NULL) {
printf("NAME OF CURRENT MOVIE TO COMPARE TO: %s\n", temp->title); // test
if(strcmp(temp->title, tempTitle) == 0) {
// match
printf("Year: %d\n", temp->year);
printf("Rating: %hhu\n", temp->rating);
found = true;
break;
} else { // no match so far
temp = temp->next;
printf("HAVEN'T FOUND MATCH, NEXT TITLE TO CHECK IS: %s\n", temp->title); // test print
found = false;
} // end else
} // end while
if(found == false) { // no match confirmed
printf("Movie \"%s\" does not exist in the database.\n", tempTitle);
}
} else { // choice is invalid
loop = 0; // exit
} // end if-else
} // end while
// free all the nodes
return 0;
}
注意:我还没有实现的唯一事情就是释放内存。.我不确定百分百应该如何实现。
任何帮助是极大的赞赏..
问题出在您的malloc()
调用上。 首先,您要做的是:
movie *head = NULL;
// ...
head = malloc(sizeof(movie));
这意味着head不再为null,您将无法以所需的方式插入第一部电影-将malloc()
移动到其他位置。
其次,执行以下几行代码:
current = head; // <- this is OK
// ...
current = malloc(sizeof(movie)); // allocate mem <- this is NOT OK, for the same reason as before
同样,您可以像这样读取电影的标题: scanf("%249s", head->title)
。
如果您知道该怎么走,请告诉我。
除了代码中的问题外,还有另一个问题: 实验室的TA也不知道哪里出了问题 。
样品修复
movie *new_node(void){//aggregate the creation of a new node
movie *node = malloc(sizeof(*node));//error check omit
printf("Name of the movie: ");
scanf(" %249[^\n]%*c", node->title);
printf("Year: ");
scanf("%d", &node->year);
printf("Rating: ");
scanf("%hhu", &node->rating);
node->next = NULL;
return node;
}
int main() {
int loop = 1;
movie *head = NULL;
movie *current;
movie *temp;
//head = malloc(sizeof(movie));//"if(head == NULL) {" don't work
int amountOfMovies = 0;
char choice;
while(loop) {
printf("%d Movie(s) in the database. Update or search (U/S): ", amountOfMovies);
scanf(" %c", &choice);
if(choice == 'U') {
if(head == NULL) {
current = head = new_node();//need set to current
} else {
current = head;
while(current->next != NULL) {//"current != NULL" can't link
current = current->next;
}
current = current->next = new_node();
}
printf("Movie \"%s\" is added to the database.\n", current->title);
amountOfMovies++;
} else if(choice == 'S') {
char tempTitle[250];
bool found = false;//need <stdbool.h>
temp = head;
//temp = malloc(sizeof(movie));//Unnecessary
printf("Name of movie: ");
scanf(" %249[^\n]%*c", tempTitle);
//printf("NAME OF MOVIE IN HEAD: %s\n", temp->title);
while(temp != NULL) {
//printf("NAME OF CURRENT MOVIE TO COMPARE TO: %s\n", temp->title);
if(strcmp(temp->title, tempTitle) == 0) {
printf("Year: %d\n", temp->year);
printf("Rating: %hhu\n", temp->rating);
found = true;
break;
} else {
temp = temp->next;
printf("HAVEN'T FOUND MATCH, NEXT TITLE TO CHECK IS: %s\n", temp->title);
//found = false;//Unnecessary
}
}
if(found == false) {
printf("Movie \"%s\" does not exist in the database.\n", tempTitle);
}
} else {
loop = 0;
}
}
// free all the nodes
return 0;
}
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.