Evaluate the number of "1" in a binary number

First lookCode:

1 # Include < Stdio. h >
2
3   Int Fun ( Int X)
4 {
5 Int Count = 0 ;
6 While (X)
7 {
8 Count ++ ;
9 X = X & (X - 1 );
10 }
11 Return Count;
12 }
13
14   Void Main ( Void )
15 {
16 Int J = 0 ;
17 Int M = 0 ;
18 J = Fun ( 9999 ); // "9999" is just an example.
19   Return ;
20 }

 

Guess what the last "J" value is? This is a Microsoft exam I saw in a document.
The value of "J" is 8.
Train of Thought: Convert "9999" to binary, and check the number of "1 ". If you still cannot understand it, use a pen to calculate it manually (in binary mode ).