耐心看完，先谢了~~

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

#define N 21

int apple[3];
char tail[3];

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

int Block(char head[2])  //判断出界
{
    if ((head[0] < 1) || (head[0] > N) || (head[1] < 1) || (head[1] > N))
        return 1;
    return 0;
}

int Eat(char snake[2])
{
    if ((snake[0] == apple[0]) && (snake[1] == apple[1]))
       {
        apple[0] = apple[1] = apple[2] = 0;
        return 1;
       }
    return 0;
}

void Draw(char **snake, int len)   //蛇移动
{
    if (apple[2]) {
        gotoxy(apple[1] * 2, apple[0]);
        printf("○");
    }

    gotoxy(tail[1] * 2, tail[0]);
    if (tail[2])
        printf("★");
    else
        printf("■");
    gotoxy(snake[0][1] * 2, snake[0][0]);
    printf("★");
    putchar('\n');
}

int Move(char **snake, char dirx, int *len)  //控制方向
{
    int i, full = Eat(snake[0]);
    memcpy(tail, snake[(*len)-1], 2);
    for (i = (*len) - 1; i > 0; --i)
        memcpy(snake[i], snake[i-1], 2);
    switch (dirx)
      {
       case 'w': case 'W': --snake[0][0]; break;
          case 's': case 'S': ++snake[0][0]; break;
       case 'a': case 'A': --snake[0][1]; break;
       case 'd': case 'D': ++snake[0][1]; break;
       default: ;
     }
    if (Block(snake[0]))  return 0;

    if (full) //  感觉 bugs is here!
       {
        snake = (char **)realloc(snake, sizeof(char *) * ((*len) + 1));
        snake[(*len)] = (char *)malloc(sizeof(char) * 2);
        memcpy(snake[(*len)], tail, 2);
        ++(*len);
        tail[2] = 1;
       }
       else
        tail[2] = 0;
    return 1;
}

void init(char plate[N+2][N+2], char ***snake_x, int *len)  //初始化
{
    int i, j;
    char **snake = NULL;

    *len = 3;
    snake = (char **)realloc(snake, sizeof(char *) * (*len));
    for (i = 0; i < *len; ++i)
        snake[i] = (char *)malloc(sizeof(char) * 2);
        
    for (i = 0; i < 3; ++i)
        {
        snake[i][0] = N/2 + 1;
        snake[i][1] = N/2 + 1 + i;
         }

    for (i = 1; i <= N; ++i)
        for (j = 1; j <= N; ++j)
            plate[i][j] = 1;
            
    apple[0] = rand()%N + 1; apple[1] = rand()%N + 1;
    apple[2] = 1;

    for (i = 0; i < N + 2; ++i)
        {
        gotoxy(0, i);
        for (j = 0; j < N + 2; ++j)
            {
            switch (plate[i][j])
                {
                 case 0: printf("□"); continue;
                    case 1: printf("■"); continue;
                 default: ;
                 }
            }
           putchar('\n');
        }
    for (i = 0; i < (*len); ++i)
       {
        gotoxy(snake[i][1] * 2, snake[i][0]);
        printf("★");
        }
    putchar('\n');
    *snake_x = snake;
}

void Manual()
{
    FILE *fp;
    //fopen
    gotoxy(N+30,1);
    printf("按 W S A D 移动方向");
    gotoxy(N+30,5);
    printf("历史最高分为: 100");
    gotoxy(N+30,8);
    printf("你现在得分为: 0");
   
}
void Free(char **snake, int len)
{
    int i;
    for (i = 0; i < len; ++i)
        free(snake[i]);
    free(snake);
}

int main(void)
{
    int len;
    char ch = 'a';
    char a[N+2][N+2] = {{0}};
    char **snake;
    srand((unsigned)time(NULL));
    init(a, &snake, &len);
    Manual();
    while (ch != 0x1B)   // 按 ESC 结束
     {
        Draw(snake, len);
        if (!apple[2]) {
            apple[0] = rand()%N + 1;
            apple[1] = rand()%N + 1;
            apple[2] = 1;
        }
        setbuf(stdin, NULL);
        if (kbhit())
           {
            gotoxy(0, N+2);
            ch = getche();
            }
        if (!Move(snake, ch, &len))
          {
            gotoxy(N+2, N+2);
            puts("你输了");
            Free(snake, len);
            exit(0);
          }
        Sleep(300);   
    }
    Free(snake, len);
    exit(0);
    return 0;
}

为什么蛇吃完第二个苹果了，程序就报错了？

void init(char plate[N+2][N+2], char ***snake_x, int *len)  //初始化
{
    int i, j;
    char **snake = NULL;
   
    *len = 3;
    snake = (char **)realloc(snake, sizeof(char *) * 9999);//

snake的第一维就是蛇身的长度，设置的足够长的话就没事。

snake = (char **)realloc(snake, sizeof(char *) * ((*len) + 1));
        snake[(*len)] = (char *)malloc(sizeof(char) * 2);//这两句会让snake丢失以前的信息。

要是改这个的话，你得使用一个for把原先的snake[0~*len-1]所指向的信息重新链回来（说的太绕口了）。还得使用free释放内存。
还有这个贪吃蛇写的挺好的。