title: going through each cell in a column and reset its value if >0
body: <p>When I open a google sheet, I'd like all values within one specific column to be reset to 0 if its value is >0.
  Please note that some cells contain no data, I wouldn't like to mess up with these cells as they should stay empty.
  At the moment I'm really trying to build up an MVP so if I have to hardcode the value of the column within the formula it's OK.</p>
  
  <p>I've made some research and tried to find relevant examples here, I've tweaked one snippet which works for one specific cell, now I'd like to learn how to automate the execution of this script so I don't have to hardcode each cell....</p>
  
  <p>Here is the script I have</p>
  
  <pre><code>function onOpen() {
      var doc = SpreadsheetApp.getActiveSpreadsheet();
      var cell = doc.getRange("B4");
      var value = cell.getValue();
  
      if (value &gt; 0) {
          cell.setValue("0");
      }
      else {
          cell.setValue("0");
      }
  } 
  </code></pre>
  
  <p>I'd really appreciate if you could help me a bit with this one by either poiting me in the right direction or showing me a working example.</p>
  
  <p>Thanks</p>