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copied!<p>In most cases, <code>&&</code> and <code>||</code> are preferred over <code>&</code> and <code>|</code> because the former are short-circuited, meaning that the evaluation is canceled as soon as the result is clear. </p> <p>Example:</p> <pre><code>if(CanExecute() && CanSave()) { } </code></pre> <p>If <code>CanExecute</code> returns <code>false</code>, the complete expression will be <code>false</code>, regardless of the return value of <code>CanSave</code>. Because of this, <code>CanSave</code> is not executed.</p> <p>This is very handy in the following circumstance:</p> <pre><code>string value; if(dict.TryGetValue(key, out value) && value.Contains("test")) { // Do Something } </code></pre> <p><code>TryGetValue</code> returns <code>false</code> if the supplied key is not found in the dictionary. Because of the short-circuiting nature of <code>&&</code>, <code>value.Contains("test")</code> is only executed, when <code>TryGetValue</code> returns <code>true</code> and thus <code>value</code> is not <code>null</code>. If you would use the <em>bitwise AND</em> operator <code>&</code> instead, you would get a <code>NullReferenceException</code> if the key is not found in the dictionary, because the second part of the expression is executed in any case.</p> <p>A similar but simpler example of this is the following code (as mentioned by TJHeuvel):</p> <pre><code>if(op != null && op.CanExecute()) { // Do Something } </code></pre> <p><code>CanExecute</code> is only executed if <code>op</code> is not <code>null</code>. If <code>op</code> is <code>null</code>, the first part of the expression (<code>op != null</code>) evaluates to <code>false</code> and the evaluation of the rest (<code>op.CanExecute()</code>) is skipped.</p> <p>Apart from this, technically, they are different, too:<br> <code>&&</code> and <code>||</code> can only be used on <code>bool</code> whereas <code>&</code> and <code>|</code> can be used on any integral type (<code>bool</code>, <code>int</code>, <code>long</code>, <code>sbyte</code>, ...), because they are bitwise operators. <code>&</code> is the <em>bitwise AND</em> operator and <code>|</code> is the <em>bitwise OR</em> operator. </p> <p>To be very exact, in C#, those operators (<code>&</code>, <code>|</code> [and <code>^</code>]) are called "Logical operators" (see the <a href="http://msdn.microsoft.com/en-us/library/ms228593.aspx">C# spec</a>, chapter 7.11). There are several implementations of these operators:</p> <ol> <li>For integers (<code>int</code>, <code>uint</code>, <code>long</code> and <code>ulong</code>, chapter 7.11.1):<br> They are implemented to compute the bitwise result of the operands and the operator, i.e. <code>&</code> is implement to compute the bitwise logical <code>AND</code> etc.</li> <li>For enumerations (chapter 7.11.2):<br> They are implemented to perform the logical operation of the underlying type of the enumeration.</li> <li>For bools and nullable bools (chapter 7.11.3 and 7.11.4):<br> The result is not computed using bitwise calculations. The result is basically looked up based on the values of the two operands, because the number of possibilities is so small.<br> Because both values are used for the lookup, this implementation isn't short-circuiting.</li> </ol>

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