c-为什么main以外的函数中的数组初始化是临时的

这是我在main和函数"checkCollisionOrFood（）"中初始化数组"turn[20]"的代码，四个值turn[0]、turn[1]、turn[2]、turn[3]在main函数中初始化为零，其余在"checkCollision OrFood"中初始化。这就是故障开始的地方。当我在"check科里sionOrFoo（）"中将turn[4]初始化为0，然后在任何地方访问它时，它在任何函数中都保持为0，但是！当我初始化下一个turn[]，即turn[5]时，turn[4]的值被耗尽。即turn[4]有垃圾值。turn[20]是全局变量，其索引"head"也是全局的。我被这个问题卡住了，请帮我摆脱它。这是我的完整代码

#include <mega8.h>
#include <delay.h>
#include <stdlib.h>
unsigned short address[]=    {0b00001111,0b00000000,0b00000000,0b00000000,
  0b00000000,0b00000000,0b00000000,0b00000000};
unsigned short turn[20];//it is declared as global variable.
unsigned short head=3;
unsigned short colHead=0;
unsigned short rowHead =3;
unsigned short rowTail=0;
unsigned short colTail=0;
unsigned short size=4;
unsigned short foodx;
unsigned short foody;
...
unsigned short checkCollisionOrFood()
{
head=(head+1)%20;
if(turn[head-1]==0){
    turn[head]=0;

/这是turn[]被初始化的地方，如果我在这里访问turn[head]，即在初始化之后，它会给出正确的值，但如果我访问它的前一个值意味着turn[head-1]，那么它会给出垃圾值/

    PORTB=255;PORTB&=~(1<<turn[4]);PORTD.7=0;delay_ms(200);PORTD.7=1;

/通过这句话，我在初始化turn[4]之后检查了turn[4]的值，这给出了正确的答案，然后在初始化turn[5]并访问turn[4]后给出了垃圾/

    rowHead=(rowHead+1)%8;
    if(!(address[colHead]&(1<<rowHead)))return 1;
    else if((address[colHead]&(1<<rowHead))&&
    (!((colHead==foody)&&(rowHead==foodx))))gameOver();
    else return 0;
    }
if(turn[head-1]==1){
    turn[head]=1;
    colHead=(colHead+1)%8;
    if(!(address[colHead]&(1<<rowHead)))return 1;
    else if((address[colHead]&(1<<rowHead))&&
    (!((colHead==foody)&&(rowHead==foodx))))gameOver();
    else return 0;
    }
}
void main(void)
{
turn[0]=0;turn[1]=0;turn[2]=0;turn[3]=0;

/turn[]的这些值无论在哪里访问都不会更改/

while (1)
  {
  if(checkCollisionOrFood())
    {
    PORTB=(address[colHead] |=1<<rowHead);
    turnOffTail();
    blink();
    }
  else
    {
    PORTB=address[colHead];
    createFood();
    blink();
    }
  }

}

Plz建议我离开它。