title: check if numbers have the same sign
body: <p>I came across this:
  <a href="https://stackoverflow.com/questions/66882/simplest-way-to-check-if-two-integers-have-same-sign">Simplest way to check if two integers have same sign?</a></p>
  
  <p>How can this be extended to more than two numbers (not necessarily integers)? Say, check if 4 numbers have the same sign (+ve or -ve).</p>
  
  <p>I don't want to use bit operations as far as possible ... only logical conditions.</p>
  
  <p>Thanks.</p>