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copied!<p>It's not a case of which is more useful...</p> <p>A <code>String</code> is a <code>String</code> - one or more characters next to eachother. If you want to <strong><em>change</em></strong> a string in someway, it will simply create more strings because they are <strong><em><a href="http://www.yoda.arachsys.com/csharp/strings.html" rel="nofollow noreferrer">immutable</a></em></strong>.</p> <p>A <code>StringBuilder</code> is a class which creates strings. It provides a means of constructing them without creating lots of reduntant strings in memory. The end result will always be a <code>String</code>.</p> <p><strong>Don't do this</strong></p> <pre><code>string s = "my string"; s += " is now a little longer"; </code></pre> <p><strong>or</strong></p> <pre><code>s = s + " is now longer again"; </code></pre> <p>That would create <strong>5</strong> strings in memory (in reality, see below).</p> <p>Do this:</p> <pre><code>StringBuilder sb = new StringBuilder(); sb.Append("my string"); sb.Append(" is now a little longer"); sb.Append(" is now longer again"); string s = sb.ToString(); </code></pre> <p>That would create <strong>1</strong> string in memory (again, see below).</p> <p>You can do this:</p> <pre><code>string s = "It is now " + DateTime.Now + "."; </code></pre> <p>This only creates <strong>1</strong> string in memory.</p> <p>As a side-note, creating a <code>StringBuilder</code> does take a certain amount of memory anyway. As a rough rule of thumb:</p> <ul> <li>Always use a <code>StringBuilder</code> if you're concatenating strings in a loop.</li> <li>Use a <code>StringBuilder</code> if you're concatenating a string more than 4 times.</li> </ul>

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