c - 使用循环将输入输入到链表中

Question

我制作这个程序是为了了解链表，因为我刚刚开始使用它们。该程序在“输入杀虫剂的数量”语句后立即终止(这是一项学校作业)。此外，我不确定如何将列表的长度限制在用户输入的大小范围内。

#include<stdio.h>

struct plants{
    int val;
    struct plants *next;
};

void printlist();

int main(){
    struct plants* head = NULL;
    struct plants* current= head;
    head = malloc(sizeof(struct plants));
    int counter,size;

    printf("Enter the number of plants\n");

    scanf("%d",&size);

    printf("Enter the amount of pesticide each plant has.\n");

    while(current!=NULL){
        scanf("%d",current->val);
        current= current->next;
    }
    return 0;
}

Answer 1

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

int main()
{
    int count = 0;
    int size = 0;        
    printf("Enter the number of plants\n");
    scanf("%d",&size);

    printf("Enter the amount of pesticide each plant has.\n");

您必须为 while 循环内的每个节点分配内存。如果您想在列表末尾添加新节点，请通过指向列表末尾指针的指针注意列表末尾。除此之外，您必须将要读取的值的地址传递给 scanf:

    struct plants * head = NULL;
    struct plants ** current = &head; // current refers there, where next node has to be placed
    while( count < size ) // do it for "size" nodes
    {
        *current  = malloc(sizeof(struct plants)); // allocate memory for the node right to target 
        scanf( "%d", &((*current)->val));          // read the data
        (*current)->next = NULL;                   // node is last node in list, so its successor is NULL
        current = &((*current)->next);             // step on forward
        count ++;                                  // increment number of nodes
    }

请注意，由于 current 的类型是 struct plants ** 此代码将新节点放入列表的第一个元素的 head并为列表的所有其他节点转到 (*current)->next。

将新节点添加到列表的头部会更容易:

    struct plants * head = NULL; // init head with NULL (this becomes end of the list)
    while( count < size ) // do it for "size" nodes
    {
        struct plants * current = malloc(sizeof(struct plants)); // allocate memory for the node 
        scanf( "%d", &current->val);       // read the data
        current->next = head;              // successor of node is head
        head = current;                    // new node is head of list
        count ++;                          // increment number of nodes
    }

这将打印您的列表:

    struct plants *temp = head;
    while( temp != NULL )
    {
        printf( "%d ", temp->val );
        temp = temp->next;
    }

不要忘记在程序结束时释放列表:

    while ( head != NULL )
    {
        struct plants *next = head->next;
        free( head );
        head = next; 
    }
    return 0;
}