我采用WASD控制移动，墙在第一行，初始的蛇在第二行。可是运行后我输入S程序却提示我撞墙了。自己实在看不出来了，有大神帮帮我吗？
#include<stdio.h>
#include<process.h>
#include<windows.h>
#include<conio.h>
#include<time.h>
#include<stdlib.h>
#define WIDTH 40
#define HEIGH 12
enum direction{
LEFT,
RIGHT,
UP,
DOWN
};
struct Food{
int x;
int y;
};
struct Node{
int x;
int y;
struct Node *next;
};
struct Snake{
int lenth;
enum direction dir;
};
struct Food *food;
struct Snake *snake;
struct Node *snode,*tail;
int SPEED=200;
int score=0;
int smark=0;
int times=0;
int STOP=0;
void Initfood();
void Initsnake();
void Eatfood();
void Addnode(int x,int y);
void move();
void draw();
void Homepage();
void keybordhit();
void Addtail();

void gotoxy(int x,int y)
{
    COORD pos;
    pos.X=x-1;
    pos.Y=y-1;
    SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE),pos);
}

void Initsnake()
{
    int i;
    snake=(struct Snake*)malloc(sizeof(struct Snake));
    tail=(struct Node*)malloc(sizeof(struct Node));
    food=(struct Food*)malloc(sizeof(struct Food));
    snake->lenth=5;
    snake->dir=RIGHT;
    for(i=2;i<=snake->lenth+2;i++)
    {
        Addnode(i,2);
    }
}

void Initfood()
{
    struct Node *p=snode;
    int mark=1;
    srand((unsigned)time(NULL));
    while(1)
    {
        food->x=rand()%(WIDTH-2)+2;
        food->y=rand()%(HEIGH-2)+2;
        while(p!=NULL)
        {   
            if((food->x==p->x)&&(food->y==p->y))
            {
                mark=0;
                break;
            }
            p=p->next;
        }
        if(mark==1)
        {
            gotoxy(food->x,food->y);
            printf("%c",3);
            break;
        }
        mark=1;
        p=snode;
    }
}

void move()
{
    struct Node *q,*p=snode;
    if(snake->dir==RIGHT);
    {
        Addnode(p->x+1,p->y);
        if(smark==0)
        {
            while(p->next!=NULL)
            {
                q=p;
                p=p->next;
            }
            q->next=NULL;
            free(p);
        }
    }
    if(snake->dir==LEFT)
    {
        Addnode(p->x-1,p->y);
        if(smark==0)
        {
            while(p->next!=NULL)
            {
                q=p;
                p=p->next;
            }
            q->next=NULL;
            free(p);
        }
    }
    if(snake->dir==UP)
    {
        Addnode(p->x,p->y-1);
        if(smark==0)
        {
            while(p->next!=NULL)
            {
                q=p;
                p=p->next;
            }
            q->next=NULL;
            free(p);
        }
    }
    if(snake->dir==DOWN)
    {
        Addnode(p->x,p->y+1);
        if(smark==0)
        {
            while(p->next!=NULL)
            {
                q=p;
                p=p->next;
            }
            q->next=NULL;
            free(p);
        }
    }
}

void Addnode(int x,int y)
{
    struct Node *newnode=(struct Node *)malloc(sizeof(struct Node));
    struct Node *p=snode;
    newnode->next=snode;
    newnode->x=x;
    newnode->y=y;
    snode=newnode;
    if(x<2||x>=WIDTH||y<2||y>=HEIGH)
    {
        STOP=1;
        gotoxy(10,19);
        printf("撞墙，游戏结束，任意键退出！\n");
        _getch();
        free(snode);
        free(snake);
        exit(0);
    }
    while(p!=NULL)
    {
        if(p->next!=NULL)
            if((p->x==x)&&(p->y==y))
            {
                STOP=1;
                gotoxy(10,19);
                printf("碰到自身，游戏结束，任意键退出！\n");
                _getch();
                free(snode);
                free(snake);
                exit(0);
            }
            p=p->next;
    }
}

void Eatfood()
{
    Addtail();
    score++;
}

void Addtail()
{
    struct Node *newnode=(struct Node *)malloc(sizeof(struct Node));
    struct Node *p=snode;
    tail->next=newnode;
    newnode->x=50;
    newnode->y=20;
    newnode->next=NULL;
    tail=newnode;
}

void draw()
{
    struct Node *p=snode;
    while(p!=NULL)
    {
        gotoxy(p->x,p->y);
        printf("%c",2);
        tail=p;
        p=p->next;
    }
    if(snode->x==food->x&&snode->y==food->y)
    {
        smark=1;
        Eatfood();
        Initfood();
    }
    if(smark==0)
    {
        gotoxy(tail->x,tail->y);
        printf("%c",' ');
    }
    else
    {
        times=1;
    }
    if((smark==1)&&(times==1))
    {
        gotoxy(tail->x,tail->y);
        printf("%c",' ');
        smark=0;
    }
    gotoxy(50,12);
    printf("食物：%d,%d",food->x,food->y);
    gotoxy(50,5);
    printf("分数：%d",score);
    gotoxy(50,7);
    printf("速度：%d",SPEED/50);
    gotoxy(15,14);
    printf("按O键加速");
    gotoxy(15,15);
    printf("按P键减速");
    gotoxy(15,16);
    printf("按空格键暂停");
}

void HideCursor()
{
    CONSOLE_CURSOR_INFO cursor_info={1,0};
    SetConsoleCursorInfo(GetStdHandle(STD_OUTPUT_HANDLE),&cursor_info);
}

void Homepage()
{
    HideCursor();
    printf("---------------------------------------\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("|\t\t\t\t      |\n");
    printf("---------------------------------------");
    gotoxy(5,13);
    printf("任意键开始游戏！按W,A,S,D控制方向");
    _getch();
    Initsnake();
    Initfood();
    gotoxy(5,13);
    printf("                                   ");
}

void keybordhit()
{
    char ch;
    if(_kbhit())
    {
        ch=getch();
        switch(ch)
        {
        case 'W':
        case'w':if(snake->dir==DOWN)
                {break;}
            else snake->dir=UP;break;
        case 'A':
        case 'a':if(snake->dir==RIGHT)
                 {break;}
            else snake->dir=LEFT;break;
        case 'S':
        case 's':if(snake->dir==UP)
                 {break;}
            else snake->dir=DOWN;break;
        case 'D':
        case 'd':if(snake ->dir==LEFT)
                 {break;}
            else snake->dir=RIGHT;break;
        case 'O':
        case 'o':if(SPEED>=150)
                 {SPEED-=50;}
            break;
        case 'P':
        case 'p':if(SPEED<=400)
                 {SPEED+=50;}
            break;
        case ' ':gotoxy(15,18);
            printf("游戏已暂停，按任意键恢复！");
            system("pause>nul");
            gotoxy(15,18);
            printf("                             ");
            break;
        default: break;
        }
    }
}

int main(void)
{
    Homepage();
    while(!STOP)
    {
        keybordhit();
        move();
        draw();
        Sleep(SPEED);
    }
    return 0;
}