#include<stdio.h>
#include<malloc.h>
struct student
{
    int num;
    struct student *link;
}stud;
  
 creat(int n)
{
    struct student *h,*p;
    int i;
    if((h=(stud *)malloc(sizeof(stud)))==NULL);
    {
        printf("not enough memory!");
        return(0);
    }
    h=NULL;
    for(i=0;i<=n;i++)
    {
         p=h;
         
        if((p=(stud *)malloc(sizeof(stud)))==NULL);

            
            
        {
            printf("内存不足！");
            return(0);
        }
        scanf("%d",&p->num);
        p->link=h;
        h=p;
    }
    }
    void main()
    {
        struct student *h;
        h=(struct student *)creat(4);
    }
   

简单修改下：
注意creat函数要有返回值，if结尾没有分号，动态分配malloc的用法。

#include<stdio.h>
#include<malloc.h>
struct student
{
    int num;
    struct student *link;
}stud;

struct student* creat(int n)
{
    struct student *h,*p;
    int i;
    if((h= (struct student *)malloc(sizeof(stud)))==NULL )
    {
        printf("not enough memory!");
        return(0);
    }
    for(i=0;i<=n;i++)
    {
        p=h;
        if((p=(struct student *)malloc(sizeof(stud)))==NULL)
        {
            printf("内存不足！");
            return(0);
        }
        scanf("%d",&p->num);
        p->link=h;
        h=p;
    }
    return h;
}
void print(struct student* h)
{
    struct student* p=h;
    printf("%d",p->num);
    p=p->link;
    while(p!=NULL)
    {
        printf("->%d",p->num);
        p=p->link;
    }
    printf("\n");
}
int main()
{
    struct student *h;
    h=creat(4);
    print(h);
    return 0;
}

 

你的程序有两个不该犯的错误！
一,IF 后面不应有分号；
二， if((h=(stud *)malloc(sizeof(stud)))==NULL);这句应改为if((h=(student *)malloc(sizeof(stud)))==NULL)
     后面相同之处都要改！
三，creat函数creat(int n)没有遵循NASI C 标准，应改为int creat(int n)
    否则在不同平台下可能会报错！
这是我改好的：

#include<stdio.h>
#include<malloc.h>
struct student
{
    int num;
    struct student *link;
}stud;
int create(int n)
{    struct student *h;struct student *p;
    int i;
    if((h=(student *)malloc(sizeof(stud)))==NULL)
    {    printf("not enough memory!");
        return(0);
    }
    h=(student *)NULL;
    for(i=0;i<=n;i++)
    {    p=h;
        if((p=(student *)malloc(sizeof(stud)))==NULL)
        {    printf("内存不足！");
            return(0);
        }
        scanf("%d",&p->num);
        p->link=h;
        h=p;
    }
}
void main()
{    struct student *h;
    h=(struct student *)create(4);
}

#include<stdio.h>
#include<malloc.h>
struct student
{
    int num;
    struct student *link;
}stud;
int create(int n)
{    struct student *h;
     struct student *p;
     int i;
     if((h=(struct student *)malloc(sizeof(stud)))==NULL)
    {    printf("not enough memory!");
        return(0);
    }
    h=(struct student *)NULL;
    for(i=0;i<=n;i++)
    {    p=h;
        if((p=(struct student *)malloc(sizeof(stud)))==NULL)
        {    printf("内存不足！");
            return(0);
        }
        scanf("%d",&p->num);
        p->link=h;
        h=p;
    }
}
void main()
{    struct student *h;
    h=(struct student *)create(4);
}

if((h=(student *)malloc(sizeof(stud)))==NULL) 改为 if((p=(struct student *)malloc(sizeof(stud)))==NULL)，否则某些编译器不通过。

以下几处同理

原来这样，明白了