title: What username & password should be entered to use SQL plus
body: <p>I am using oracle 12c sometimes I need to use SQL plus.
  When I start sqlplus, it ask me for a username and password
  <a href="https://i.stack.imgur.com/Lb3fv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Lb3fv.png" alt="enter image description here"></a></p>
  
  <p>I used SYSTEM and SYS as users but don't work with me .Anybody has a solution please</p>