面試系列1返回整數(shù)中為1的位數(shù)

原題： write the function int bitcount(short input) that takes a short as input and
     returns an int. the function returns the number of bits set in the input
     variable. for instance:
     bitcount(7) --> 3
     bitcount(2543) --> 9
     bitcount(11111) --> 9
    代碼：
    /********************************************************************
     created: 2006/06/14
     created: 14:6:2006 16:53
     filename: c:/documents and settings/administrator/my documents/近期閱讀/mytinything/bitcount.c
     file path: c:/documents and settings/administrator/my documents/近期閱讀/mytinything
     file base: bitcount
     file ext: c
     author: a.tng
     version: 0.0.1
     purpose: 面試題
     write the function int bitcount(short input) that takes a short as input and
     returns an int. the function returns the number of bits set in the input
     variable. for instance:
     bitcount(7) --> 3
     bitcount(2543) --> 9
     bitcount(11111) --> 9
    *********************************************************************/
    #include
    /*
     * name: bitcount
     * params:
     * input [in] 需要分析的 short 型數(shù)
     * return:
     * 輸入?yún)?shù) input 的為1的位數(shù)
     * notes:
     * 計(jì)算 input 中為1的位數(shù)
     * author: a.tng 2006/06/14 17:00
     */
    int bitcount(short input)
    {
     int n_ret = 0;
     /* 只要 input 不為0，則循環(huán)判斷 */
     while (0 != input)
     {
     /* 如果 input & 1 == 1 則表示最低位為1，反之則等于0 */
     if (input & 1)
     {
     n_ret++;
     }
     input = input >> 1;
     }
     return n_ret;
    }
    /*
     * name: main
     * params:
     * none
     * return:
     * 函數(shù)返回狀態(tài)給系統(tǒng)
     * notes:
     * 系統(tǒng) main 函數(shù)
     * author: a.tng 2006/06/14 17:04
     */
    int main()
    {
     /* 輸入需要計(jì)算的整數(shù) */
     int n = 2543;
     /* 輸出 bitcount 的結(jié)果 */
     printf('%d/n', bitcount((short) n));
     /* 發(fā)送 pause 命令給系統(tǒng) */
     system('pause');
    }