怎样创建一个链表
struct student *create()
{
    struct student *head,*p1,*p2;
    int i=0,n;
    head=NULL;
    printf("plaese input n:");
    scanf("%d",&n);
    p1=((struct student *)malloc(sizeof(struct student)));
    p2=((struct student *)malloc(sizeof(struct student)));
    scanf("%d",&p1->num);
     //scanf("%s",p1->name);
     //fflush(stdin);
    // printf("plase input sex,f-女,m-男:");
    // scanf("%c",&p1->sex);
     //fflush(stdin);
     //scanf("%d",&p1->old);
    for(i=0;i<n;i++)
    {   
        if(i==0)
            head=p1;
        else{
             p1->next=NULL;
            p2->next=p1;
            p2=p1;
        }
   p1=(struct student *)malloc(sizeof(struct student));

    scanf("%d",&p1->num);
   }
  
   
    free(p1);
    return(head);

    }

红色我认为你不对的地方，蓝色是我修改后的。不理解再问吧。

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

typedef struct student
{
    int  num;
    char name[20];
    char sex;
    int  old;
    struct student *next;
} STUDENT, *PSTUDENT;


PSTUDENT _Create()
{
    PSTUDENT head=NULL, p1=NULL, p2=NULL;
    int i=0,n;
    head=NULL;
    printf("plaese input n: ");
    scanf("%d",&n);
    for(i=0; i<n; i++)
    {
        p1=(PSTUDENT)malloc(sizeof(STUDENT));
        printf("\nplase input ID:%d\n", i+1); 
        fflush(stdin);
        printf("num     : "); scanf("%d",&p1->num);
        fflush(stdin);
        printf("name    : "); scanf("%s",p1->name);
        fflush(stdin);
        printf("sex(m/f): "); scanf("%c",&p1->sex);
        fflush(stdin);
        printf("old     : "); scanf("%d",&p1->old);
        p1->next = NULL;
        if (i==0)
        {
            head = p1;
            p2 = p1;
        }
        else
        {
            p2->next = p1;
            p2 = p1;
        }
    }
    return(head);
}

void _Free(PSTUDENT head)
{
    PSTUDENT p;
    while(head != NULL)
    {
        p = head->next;
        free(head);
        head = p;
    }
}

void _List(PSTUDENT p)
{
    for (int i=1; p!=NULL; i++)
    {
        printf("\nList ID:%d\n", i); 
        printf("num     : %d\n", p->num);
        printf("name    : %s\n", p->name);
        printf("sex(m/f): %c\n", p->sex);
        printf("old     : %d\n", p->old);
        p = p->next;
    }
}

main()
{
    PSTUDENT head = _Create();
    if (head != NULL)
    {
        _List(head);
        _Free(head);
    }
}