研究贪吃蛇，为什么要两个一样的语句

#include<stdio.h>
#include<stdlib.h>
#include<windows.h>
#include<conio.h>
#include<time.h>
#define width 60
#define hight 25
#define SNAKESIZE 200//蛇身的最长长度

int key=72;//初始化蛇的运动方向，向上
int changeflag=1;//用来标识是否生成食物，1表示蛇还没吃到食物，0表示吃到食物
int speed=0;//时间延迟
struct {

int len;
//用来记录蛇身每个方块的坐标
int x[SNAKESIZE];
int y[SNAKESIZE];
int speed;

}snake;

struct
{
int x;int y;
}food;
void gotoxy(int x,int y)//调用Windows的API函数，可以在控制台的指定位置直接操作，这里可暂时不用深究
{
COORD coord;
coord.X = x;
coord.Y = y;
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
}
//■○
void drawmap()
{
//打印图框
for (int _y = 0; _y < hight; _y++)
{
for (int x = 0; x < width; x+=2)
{
if (x == 0 || _y == 0 || _y == hight - 1 || x == width - 2)
{
gotoxy(x, _y);
printf("■");
}
}
}
//打印蛇头
snake.len=3;
snake.x[0]=width/2;
snake.y[0]=hight/2;
gotoxy(snake.x[0],snake.y[0]);
printf("■");
//打印蛇身
for(int i=1;i<snake.len;i++)
{
snake.x[i]=snake.x[i-1];
snake.y[i]=snake.y[i-1]+1;
gotoxy(snake.x[i],snake.y[i]);
printf("■");
}
//初始化食物的位置
food.x=20;
food.y=20;
gotoxy(food.x,food.y);
printf("○");
}

/*
*控制台按键所代表的数字
*“↑”：72
*“↓”：80
*“←”：75
*“→”：77
*/
void snake_move()//按键处理函数
{
int history_key=key;
if (_kbhit())
{
fflush(stdin);
key = _getch();
key = _getch();
}
if(changeflag==1)//还没吃到食物，把尾巴擦掉
{
gotoxy(snake.x[snake.len-1],snake.y[snake.len-1]);
printf(" ");
}
for(int i=snake.len-1;i>0;i--)
{
snake.x[i]=snake.x[i-1];
snake.y[i]=snake.y[i-1];
}
if(history_key==72&&key==80) key=72;
if(history_key==80&&key==72) key=80;
if(history_key==75&&key==77) key=75;
if(history_key==77&&key==75) key=77;
switch(key)
{
case 72:snake.y[0]--;break;
case 75:snake.x[0]-= 2;break;
case 77:snake.x[0]+= 2;break;
case 80:snake.y[0]++;break;
}
gotoxy(snake.x[0],snake.y[0]);
printf("■");
gotoxy(0,0);
changeflag=1;
}
void creatfood()
{
if(snake.x[0] == food.x && snake.y[0] == food.y)//只有蛇吃到食物，才能生成新食物
{
changeflag=0;
snake.len++;
if(speed<=100)speed+=10;
while(1)
{
srand((unsigned int) time(NULL));
food.x=rand()%(width-6)+2;//限定食物的x范围不超出围墙，但不能保证food.x为偶数
food.y=rand()%(hight-2)+1;
for(int i=0;i<snake.len;i++)
{
if(food.x==snake.x[i]&&food.y==snake.y[i])//如果产生的食物与蛇身重合则退出
break;
}
if(food.x%2==0) break;//符合要求，退出循环
}
gotoxy(food.x,food.y); printf("○");
}
}

bool Gameover()
{
//碰到围墙，OVER
if(snake.x[0]==0||snake.x[0]==width-2)return false;
if(snake.y[0]==0||snake.y[0]==hight-1) return false;
//蛇身达到最长，被迫OVER
if(snake.len==SNAKESIZE) return false;
//头碰到蛇身，OVER
for(int i=1;i<snake.len;i++)
{
if(snake.x[0]==snake.x[i]&&snake.y[0]==snake.y[i])
return false;
}
return true;
}
int main()
{
system("mode con cols=60 lines=27");
drawmap();
while(Gameover())
{
snake_move();
creatfood();
Sleep(350-speed);//蛇的移动速度
}
return 0;
}