title: How to conditioning a data step in SAS
body: <p>I'm inside a big <code>call execute</code> and I have to do a data step only if a flag variable is <code>0</code> and not <code>1</code>.
  That is, if <code>flag=1</code> then the data step begin, otherwise not.
  So I should use <code>IF</code> outside of a <code>macro</code> and outside a data step.
  How can I fix?</p>
  
  <p>thanks in advance</p>