原文，这是一个建立链表的小程序：出了很多警告和一个错误，麻烦各位大大办忙看看并且解释一下存在的问题，感激不尽！

#include<stdio.h>
#include<malloc.h>
#define NULL 0;
struct student
{
    int age;
    char name[20];
    float score;
    struct student *next
};
void main()
{
    int i;
    struct student *p,*head,*p1;
    for(i=0;i<3;i++)
    {
        if(i=0)head=p1=p=(struct student *)malloc(sizeof(struct student));
        else
        {
        p=(struct student *)malloc(sizeof(struct student));
        if(i=1)head->next=p1=p;
        if(i=2){p1->next=p;p->next=NULL;}
        }
    printf("please input the student information:\n");
    scanf("%20s,%3d,%5f",&p->name,&p->age,&p->score);
    p=head;
    };
   
   
    do
    {printf("%s's age is %d, score is%f",p->name,p->age,p->score);
    p=p->next;
    }while(p!=NULL);
   
}





提示的错误信息：

gcc -Wall -c "node.c" (在目录/home/gmtianxia/桌面/编程练习中)
编译失败
node.c:3:1: warning: "NULL" redefined
In file included from /usr/include/malloc.h:25,
                 from node.c:2:
/usr/lib/gcc/i486-linux-gnu/4.4.1/include/stddef.h:400:1: warning: this is the location of the previous definition
node.c:10: warning: no semicolon at end of struct or union
node.c:11: warning: return type of ‘main’ is not ‘int’
node.c: In function ‘main’:
node.c:17: warning: suggest parentheses around assignment used as truth value
node.c:21: warning: suggest parentheses around assignment used as truth value
node.c:22: warning: suggest parentheses around assignment used as truth value
node.c:25: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[20]’
node.c:33: error: expected ‘)’ before ‘;’ token

谢谢楼上帮顶，继续求助大虾们～

发现  if(i=0) 错了，应该为if（i==0) 郁闷～     但是后面的scanf("%20s,%3d,%5f",&p->name,&p->age,&p->score);和  do
    {printf("%s's age is %d, score is%f",p->name,p->age,p->score);
    p=p->next;
    }while(p!=NULL);

还是看不出问题， 各位大小虾请指教
！

楼上的仙女太伟大了～   能解释一下 为什么 //#define NULL 0;//这里不需要定义NULL为0 吗？  课本里有些题目这样定义是为什么~?

谢谢！ 这个论坛太强大了～ 高手多，重要的是热心的高手多！顶！