/*创建链表*/
#include<stdio.h>
#include<stdlib.h>
struct list
{
    int data;
    struct list *next;
};
typedef struct list node;
typedef node *link;
void main()
{
    link ptr,head;
    int num,i;
    head=(link)malloc(sizeof(node));
    ptr=head;
    printf("please input five numbers\n");
    for(i=0;i<=4;i++)
    {
        scanf("%d",&num);
        ptr->data=num;
        ptr->next=(link)malloc(sizeof(node));
        if(i==4)
            ptr->next=NULL;
        else ptr=ptr->next;
    }
    ptr=head;
    while(ptr!=NULL)
    {
        printf("The number is %d\n",ptr->data);
        ptr=ptr->next;
    }
}

加粗，加下划线的两个语句功能有何区别，为什么要两次使用？