// que.c -- use C to inplement Queue as a circular queue
enum{ NELEMENT=99 };  // good habit
static long data[NELEMENT];
static int phead=0, ptail=0;   // phead 指向 queue 的前頭, ptail指向尾巴
initQueue(void){ phead = ptail = 0; }
void enque(long);
long deque(void);
long front(void) { return data[phead]; }
int isempty(void) { return (phead == ptail) ;}
int isfull(void) { return ((ptail+1) % NELEMENT) == phead; } //留一個不用!
////// //////
 void push(long x) { enque(x); }
 long pop(void) { return deque( ); }
 long top(void) { return front( ); }
 int empty(void) { return isempty( );}
 int full(void) { return isfull( );}
/////// /////// /////// /////// /////// /////// 
void enque(long x) {
    if( isfull() ) { return; }  // may want to give some error message?
    data[ptail] = x;
    ptail++;
    ptail %=  NELEMENT;    /* x %= y;  means x = x % y; */
}
long deque(void) {  
   if( !isempty() ) {
      long tmp=data[phead];
      phead++; phead %= NELEMENT;
      return tmp;
   } // if !isempty
}