title: What is side effect in C?
body: <p>Wikipedia says that:</p>
  
  <blockquote>
    <p><em>In computer science, an operation, function or expression is said to have a <strong>side effect</strong> if it modifies some state variable value(s) outside its local environment, that is to say has an observable effect besides returning a value (the main effect) to the invoker of the operation.</em></p>
  </blockquote>
  
  <p>But how can we access a variable outside its local environment, can anyone explain this situation, side effect, main effect and sequence point comprehensibly?</p>