c语言贪吃蛇，部分代码，运行与理论上不同？

代码敲了一半了，但是运行的结果和理论上不一样
运行以下代码，应该会在中间出现一条小蛇，小蛇默认头向右，wsad控制方向
但是运行后小蛇没有动，然后就按任意键退出了
问题在哪？

#include<stdio.h>
#include<windows.h>
#include<conio.h>
#include<stdlib.h>

#define HIGH 25
#define WIDTH 60

int moveDirection;              //小蛇移动方向，1,2,3,4分别表示上下左右
int canvas[HIGH][WIDTH] = {0};  
//0为空格，-1为边框#，1为蛇头@，>1为蛇身*

void HideCursor()
{
    CONSOLE_CURSOR_INFO cursor_info={1,0};//第二个值为0表示隐藏光标
    SetConsoleCursorInfo(GetStdHandle(STD_OUTPUT_HANDLE),&cursor_info);
}

void gotoxy(int x,int y)//光标移动到(x,y)位置
{
    HANDLE handle = GetStdHandle(STD_OUTPUT_HANDLE);
    COORD pos;
    pos.X = x;
    pos.Y = y;
    SetConsoleCursorPosition(handle,pos);
}

void startup()
{
    int i,j;

    //以下设置边框
    for(i=0;i<HIGH;i++)
    {
        canvas[i][0] = -1;
        canvas[i][WIDTH-1] = -1;
    }
    for(j=0;j<WIDTH;j++)
    {
        canvas[0][j] = -1;
        canvas[HIGH-1][j] = -1;
    }

    //以下设置蛇
    canvas[HIGH/2][WIDTH/2] = 1;
    
    for(i=0;i<=4;i++)
        canvas[HIGH/2][WIDTH/2-i] = i+1;

    moveDirection = 4;

    HideCursor();//隐藏光标
}

void moveSnake()
{
    int i,j;
    int max = 0;
    int oldtail_i,oldtail_j;    //旧蛇尾位置
    int oldhead_i,oldhead_j;    //旧蛇头位置
    int newhead_i,newhead_j;    //新蛇头位置

    for(i=1;i<HIGH-1;i++)
        for(j=1;WIDTH-1;j++)
        {
            if(canvas[i][j]>0)      //对所有大于零的元素加一
            {
                canvas[i][j]++;

                if(max<canvas[i][j])    //求出最大值
                {
                    max = canvas[i][j];
                    oldtail_i = i;      //旧蛇尾位置
                    oldtail_j = j;
                }

                if (canvas[i][j]==2)
                {
                    oldhead_i = i;      //旧蛇头位置
                    oldhead_j = j;
                }
            }
        }
        canvas[oldtail_i][oldtail_j] = 0;   //最大值所在元素变为0
        
        if(moveDirection == 1)      //向上
        {
            canvas[oldhead_i-1][oldhead_j] = 1;
            newhead_i = oldhead_i-1;
            newhead_j = oldhead_j;
        }
        
        if(moveDirection == 2)      //向下
        {
            canvas[oldhead_i+1][oldhead_j] = 1;
            newhead_i = oldhead_i+1;
            newhead_j = oldhead_j; 
        }
        
        if(moveDirection == 3)      //向左
        {
            canvas[oldhead_i][oldhead_j-1] = 1;
            newhead_i = oldhead_i;
            newhead_j = oldhead_j-1;
        }

        if(moveDirection == 4)      //向右
        {
            canvas[oldhead_i][oldhead_j+1] = 1;
            newhead_i = oldhead_i;
            newhead_j = oldhead_j+1;
        }
}

void show()
{
    int i,j;
    gotoxy(0,0);
    
    for(i=0;i<HIGH;i++)
    {
        for(j=0;j<WIDTH;j++)
        {
            if(canvas[i][j] == 0)
                printf(" ");        //输出空格
            else if(canvas[i][j] == -1)
                printf("#");        //输出边框
            else if(canvas[i][j] == 1)
                printf("@");        //输出蛇头
            else if(canvas[i][j] > 1)
                printf("*");        //输出蛇身
        }
        printf("\n");
    }

    Sleep(100);
    
}

void updateWithoutInput()
{
    moveSnake();
        
}

void updateWithInput()
{   
    char input;

    if(kbhit())
    {
        input = getch();
        
        if(input=='a')
            moveDirection = 3;
    
        if(input=='d')
            moveDirection = 4;
    
        if(input=='w')
            moveDirection = 1;
    
        if(input=='s')
            moveDirection = 2;
    }
    
}

int main()
{
    startup();//游戏初始化
    while(1)
    {
        show();//显示画面
        updateWithoutInput();//与用户输入无关的更新
        updateWithInput();//与用户输入有关的更新
    }

    return 0;
}