title: What are preconditions and postconditions?
body: <p>I'm learning how to program but one thing I can't quite get my head around is preconditions and <strong>postconditions</strong>.</p>
  
  <p>Is an if statement before calling a function considered a <strong>precondition</strong>, or is there a separate more efficient way of doing this in most languages?</p>
  
  <p>I'm also struggling to find any examples of <strong>preconditions</strong> that I could understand with my current knowledge of programming if anyone could prove a simple one then I would really appreciate it (any language will be fine)</p>