알고리즘 컴파일...

링크드 리스트 알고리즘 짜보았는데...

/*link.h*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct _slist List;
typedef struct _slist{
        int num;
        List *next;
        List *prev;
}List;

/*link.c*/
#include "link.h"
void ShowList(List *plist)
{
        List *p;
        p=plist;

        while(p)
        {
        printf("%d\n",p->num);
        p=p->next;
        }
}
void main()
{
        List *pList,*pNew,*pIns;
        pList=(List *)malloc(sizeof(List));
        pList->next=0;
        pList->prev=0;
        pList->num=1;
        printf("root생성시\n");
        ShowList(pList);
        pNew=(List *)malloc(sizeof(List));
        pList->next=pNew;
        pNew->prev=pList;
        pNew->next=0;
        pNew->num=2;

        printf("pNew생성시\n");
        ShowList(pList);

        pIns=(List *)malloc(sizeof(List));
        pIns->num=3;
        pIns->prev=pList;
        pIns->next=pNew;
        pList->next=pIns;
        pNew->prev=pIns;
        printf("pIns생성시\n");
        ShowList(pList);

        pList->next=pNew;
        pNew->prev=pList;
        free(pIns);
        printf("pIns 삭제시\n");
        ShowList(pList);
        free(pNew);
        free(pList);
}

컴파일 에러가 났습니다

에러내역은

link.h:9: redefinition of `List'
link.h:4: `List' previously declared here
link.c: In function `main':
link.c:14: warning: return type of `main' is not `int'
이렇습니다 에러를 잡지 못하겠습니다
많은분들 도움 바람니다 그리고
link.h에서

/*link.h*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct _slist{
        int num;
        slist *next;
        slist *prev;
}List;

이렇게 바꾸었더니 에러가...
In file included from link.c:1:
link.h:6: parse error before "_slist"
link.h:6: warning: no semicolon at end of struct or union
link.h:7: warning: data definition has no type or storage class
link.h:8: parse error before '}' token
link.h:8: warning: data definition has no type or storage class
link.c:2: parse error before '*' token
link.c: In function `ShowList':
link.c:4: `p' undeclared (first use in this function)
link.c:4: (Each undeclared identifier is reported only once
link.c:4: for each function it appears in.)
link.c:5: `plist' undeclared (first use in this function)
link.c: In function `main':
link.c:15: `pList' undeclared (first use in this function)
link.c:15: `pNew' undeclared (first use in this function)
link.c:15: `pIns' undeclared (first use in this function)
link.c:16: parse error before ')' token
link.c:22: parse error before ')' token
link.c:31: parse error before ')' token
link.c:14: warning: return type of `main' is not `int'

차이점이 먼지 알고싶습니다

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