将如表21.1所示的学生信息建立成一个按学号升序有序的链表，每个节点包括学号、姓名、性别、年龄。统计链表中年龄小于20的学生个体数并将对应的学生信息（包括学号、姓名、性别、年龄）输出
代码如下：
#include"stdio.h"
#include"stdlib.h"
#include"string.h"
void main()
{
    struct student
    {
        int id;
        char name[10];
        char x;
        int age;
        struct student *next;
    };
    struct student *head,*tail;
    void lianbiao(struct student *stu)
    {//第16行
        stu=(struct student *)malloc(sizeof(struct student));
        head=tail=stu;
        stu->next=NULL;
    }
    void jialianbiao(int idd,char *namee,char xx,int agee)
    {//22行
        struct student *ss=(struct student *)malloc(sizeof(struce student));
        ss->id=idd
            strcpy(ss->name,namee);
        ss->x=xx;
        ss->age=agee;
        tail->next=ss;
        ss->next=NULL;
        tail=ss;
    }
    void tlianbiao()
    {//33行
        struct student *now;
        now=head->next;
        while(now!=NULL)
        {
            if(now->age<20)
                printf("%5d%5s%5c%5d\n",now->id,now->name,now->x,now->age);
            now=now->next;
        }
    }
    void destroy()
    {//44行
        struct student *now;
        now=head;
        while(now!=NULL)
        {
            head=now->next;
            free(now);
            now=head;
        }
    }
    int main()
    {//55行
    struct student *stu;
    liaobiao(stu);
    jialianbiao(305001,"Zhang",'M',18);
    jialianbiao(305002,"Wang",'F',20);
    jialianbiao(305003,"Li",'F',19);
    jialianbiao(305004,"Zhao",'M',21);
    printf("学号     姓名     性别     年龄\n");
    tlianbiao();
    destroy();
    return 0;
    }
}
有如下错误
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(16) : error C2601: 'lianbiao' : local function definitions are illegal
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(22) : error C2601: 'jialianbiao' : local function definitions are illegal
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(33) : error C2601: 'tlianbiao' : local function definitions are illegal
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(44) : error C2601: 'destroy' : local function definitions are illegal
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(55) : error C2556: 'int __cdecl main(void)' : overloaded function differs only by return type from 'void __cdecl main(void)'
        C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(4) : see declaration of 'main'
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(55) : error C2371: 'main' : redefinition; different basic types
        C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(4) : see declaration of 'main'
C:\Users\Administrator\Desktop\新建文件夹\链表.cpp(55) : error C2601: 'main' : local function definitions are illegal
执行 cl.exe 时出错.


为什么错了？明明定义没啥问题啊？