判断给定十进制整数的二进制形式中含有几个1

 1 unsigned int_number( int n)
 2 {
 3     if (n < 0)
 4         return;
 5     unsigned count = 0;
 6     while (n != 0)
 7     {
 8         if ((n & 1) != 0)
 9             ++count;
10         n >>= 1;
11     }
12     return count;
13 }
14 
15 unsigned int_number2(int n)
16 {
17     unsigned count = 0;
18     int factor = 1;
19     while (factor > 0)
20     {
21         if ( (n & factor) != 0 )
22             ++count;
23         factor <<= 1;
24     }
25     if (n < 0)
26         ++count;
27     return count;
28 }
29 
30 int main()
31 {
32     cout << "Please enter an integer: ";
33     int num;
34     cin >> num;
35     cout << num << " contains " << int_number(num) << " 1." << endl;
36     cout << num << " contains " << int_number2(num) << " 1." << endl;
37 
38     return 0;
39 }