/*
  求出小於1000的質數（第四版）
*/
#include  <stdio.h>
 
int main(void)
{
    int     i, no;
    int     prime[500];                     /* 儲存質數的陣列 */
    int     ptr = 0;                        /* 已知質數的個數 */
    unsigned long  counter = 0;
 
    prime[ptr++] = 2;                       /* 2是質數 */
    prime[ptr++] = 3;                       /* 3也是質數 */
 
    for (no = 5 ; no <= 1000; no += 2) {    /* 以奇數為對象 */
        for (i = 1; i < ptr; i++) {         /* 將已知奇數再拿來除 */
            counter++;
            if (no % prime[i] == 0)	        /* 若可以整除就不是質數 */
	break;            	                    /* 至此不要再重複操作 */
       }
       if (ptr == i)		                /* 最後仍不能整除 */
            prime[ptr++] = no;	            /* 增加至陣列中 */
  }
  for (i = 0; i < ptr; i++)
       printf("%d\n", prime[i]);
 
  printf("乘除的次數：%lu\n", counter);
 
  return (0);
}
 

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