title: What does fopen() return to the file pointer if file is opened?
body: <p>For example if we declare a file pointer <code>fp</code> and open a file like this:<br>
  <code>FILE* fp = fopen("filename","w");</code></p>
  
  <p>If the file doesn't open <code>fopen</code> returns <code>NULL</code> to file pointer <code>fp</code>. What is stored in the file pointer <code>fp</code> if the file opens?</p>