title: Replace string spaces with an underscore
body: <p>I need to replace some spaces with an underscore (i.e. "PM HD PSP" > "PM_HD_PSP")</p>
  
  <p>Here's what I've tried so far:</p>
  
  <pre><code>private string NombreExcel3(string excel)
  {
      MessageBox.Show(excel);
  
      excel.Replace(' ','_');
  
      MessageBox.Show(excel);
      return excel;
  }
  </code></pre>