以下例子主要在說明如何在純種 C 語言中實作出一個佇列(Queue, 排隊),
至於 Queue 的定義以及用途請參考計概課本或是資料結構課本,
或者用 google.com 找一找應該也可看到許多實例與說明!

tsaiwn@magpie % cat -n que.c
     1	// que.c -- use C to inplement Queue as a circular queue
     2	enum{ NELEMENT=99 };  // good habit
     3	static long data[NELEMENT];
     4	static int phead=0, ptail=0; // phead 指向queue的前頭, ptail指向尾巴
     5	initQueue(void){ phead = ptail = 0; }
     6	void enque(long);
     7	long deque(void);
     8	long front(void) { return data[phead]; }
     9	int isempty(void) { return (phead == ptail) ;}
    10	int isfull(void) { return ((ptail+1) % NELEMENT) == phead; } //留一個不用!
    11	////// //////
    12	 void push(long x) { enque(x); }
    13	 long pop(void) { return deque( ); }
    14	 long top(void) { return front( ); }
    15	 int empty(void) { return isempty( );}
    16	 int full(void) { return isfull( );}
    17	/////// /////// /////// /////// /////// /////// 
    18	void enque(long x) {
    19	    if( isfull() ) { return; }  // may want to give some error message?
    20	    data[ptail] = x;
    21	    ptail++;
    22	    ptail %=  NELEMENT;    /* x %= y;  means x = x % y; */
    23	}
    24	long deque(void) {
    25	   if( !isempty() ) {
    26	      long tmp=data[phead];
    27	      phead++; phead %= NELEMENT;
    28	      return tmp;
    29	   } // if !isempty
    30	}
tsaiwn@magpie % gcc -c que.c        <=== 要求只要生出機器碼檔案 que.o
tsaiwn@magpie % nm que.o          <=== 要求列出 que.o 內的 symbols
0000018c C data
000000f4 T deque
0000009e T empty
000000b2 T enque
00000019 T front
000000a8 T full
00000000 T initQueue
0000002a T isempty
00000040 T isfull
00000000 D phead
00000087 T pop
00000004 D ptail
00000071 T push
00000094 T top
tsaiwn@magpie % cat -n tstque.c
     1	/// tstque.c -- example to use the circular Queue written in C language
     2	// by Wen-Nung Tsai, tsaiwn@csie.nctu.edu.tw
     3	// gcc -c que.c
     4	// gcc tstque.c que.o ; ./a.out
     5	/**********************************/
     6	#include <stdio.h>
     7	int main( ) {
     8	   printf("Test queue written in C Language.\n");
     9	   enque(53);
    10	   enque(770);
    11	   enque(880);
    12	   while( !isempty( ) ) {
    13	      printf("%ld ", deque( ) );
    14	   }
    15	   printf("\n===bye\n");
    16	   return 0;
    17	}
tsaiwn@magpie % gcc tstque.c que.o
tsaiwn@magpie % ./a.out
Test queue written in C Language.
53 770 880
===bye
tsaiwn@magpie % echo p621