原题：
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
代码：
/********************************************************************
created: 2006/06/14
created: 14:6:2006 16:53
filename: C:\Documents and Settings\Administrator\My Documents\近期阅读\myTinyThing\bitCount.c
file path: C:\Documents and Settings\Administrator\My Documents\近期阅读\myTinyThing
file base: bitCount
file ext: c
author: A.TNG
version: 0.0.1
purpose: 面试题
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 <stdio.h>
/*
* name: bitCount
* params:
* input [in] 需要分析的 short 型数
* return:
* 输入参数 input 的为1的位数
* notes:
* 计算 input 中为1的位数
* author: A.TNG 2006/06/14 17:00
*/
int bitCount(short input)
{
int n_ret = 0;
/* 只要 input 不为0，则循环判断 */
while (0 != input)
{
/* 如果 input & 1 == 1 则表示最低位为1，反之则等于0 */
if (input & 1)
{
n_ret++;
}
input = input >> 1;
}
return n_ret;
}
/*
* name: main
* params:
* none
* return:
* 函数返回状态给系统
* notes:
* 系统 main 函数
* author: A.TNG 2006/06/14 17:04
*/
int main()
{
/* 输入需要计算的整数 */
int n = 2543;
/* 输出 bitCount 的结果 */
printf("%d\n", bitCount((short) n));
/* 发送 PAUSE 命令给系统 */
system("PAUSE");
}