title: Batch file missing operand error, but output is correct
body: <p>I have made a batch file that adds a user input number to a number stored in a text file.
  The file <code>num1.txt</code> contains <code>268</code>. I open cmd and type <code>addToNum num1 20</code> and I get <code>Missing operand.</code> But when I open <code>num1.txt</code> again, it now contains <code>288</code>. So the command works, but still I get the error.<br />
  <br />
  This is my script:</p>
  <pre><code>@echo off
  set /a value = &lt; C:\path\to\file\%1.txt
  set /a value = %value% + %2
  echo %value% &gt; C:\path\to\file\%1.txt
  </code></pre>
  <p>What is the problem? And why doesn't it affect the output?</p>