Problems related to bit operations

Bitwise calculation problem // debug (8 & nbsp; & amp; & nbsp; 15); // 8 $ a & nbsp ;=& nbsp; $ this-& gt; list; // 8 $ B & nbsp ;=& nbsp; $ right [$ modular [$ I] ['m _ id']; // 15 echo & nbs bit operation problems
// Debug (8 & 15); // 8
$ A = $ this-> list; // 8
$ B = $ right [$ modular [$ I] ['m _ id']; // 15
Echo $ a; // 8
Echo"
";
Echo $ B; // 15
Debug ($ a & $ B); // 0

The debug () function is the output result.

The problem is why when we use variables instead of 8 and 15, the calculation becomes 0.
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Debug ($ a & $ B ));

Try this result.
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What is debug function? Custom?
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$ A = $ this-> list; // 8
$ B = $ right [$ modular [$ I] ['m _ id']; // 15

Are the two really 8 and 15?
I don't have debug. after echo, the result is 8.
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Can you reply? new guy.