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    <p><strong>First Question:</strong></p> <p>A <code>|</code> does a bitwise or; a bit will be set in the result if it is set in the first value or the second value. (You use it on <code>enums</code> to create values that are combinations of other values) If you were to use a bitwise and, it wouldn't make very much sense.</p> <p>It gets used as follows:</p> <pre><code>[Flags] enum FileAccess{ None = 0, // 00000000 Nothing is set Read = 1, // 00000001 The read bit (bit 0) is set Write = 2, // 00000010 The write bit (bit 1) is set Execute = 4, // 00000100 The exec bit (bit 2) is set // ... ReadWrite = Read | Write // 00000011 Both read and write (bits 0 and 1) are set // badValue = Read &amp; Write // 00000000 Nothing is set, doesn't make sense ReadExecute = Read | Execute // 00000101 Both read and exec (bits 0 and 2) are set } // Note that the non-combined values are powers of two, \ // meaning each sets only a single bit // ... // Test to see if access includes Read privileges: if((access &amp; FileAccess.Read) == FileAccess.Read) </code></pre> <p>Essentially, you can test if certain bits in an <code>enum</code> are set; in this case we are testing to see if the bits corresponding to a <code>Read</code> are set. Values <code>Read</code> and <code>ReadWrite</code> would both pass this test (the both have bit zero set); <code>Write</code> would not (it does not have bit zero set).</p> <pre><code>// if access is FileAccess.Read access &amp; FileAccess.Read == FileAccess.Read // 00000001 &amp; 00000001 =&gt; 00000001 // if access is FileAccess.ReadWrite access &amp; FileAccess.Read == FileAccess.Read // 00000011 &amp; 00000001 =&gt; 00000001 // uf access is FileAccess.Write access &amp; FileAccess.Read != FileAccess.Read // 00000010 &amp; 00000001 =&gt; 00000000 </code></pre> <p><strong>Second Question:</strong></p> <p>I think when you say "and/or", you mean "one, the other or both". This is exactly what the <code>||</code> (or operator) does. To say "one or the other, but not both", you'd use <code>^</code> ( the exclusive or opertor).</p> <p>Truth tables (true==1, false==0):</p> <pre><code> A B | A || B ------|------- OR 0 0 | 0 0 1 | 1 1 0 | 1 1 1 | 1 (result is true if any are true) A B | A ^ B ------|------- XOR 0 0 | 0 0 1 | 1 1 0 | 1 1 1 | 0 (if both are true, result is false) </code></pre>
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