IN CASE - UNLESS

• In case
  
  In case expresses the possibility of something happening.
  It is used to express the idea of doing something to avoid a possible problem later on.
  It gives the reason for an action.
  
  
  • Take an umbrella in case it rains.
    = There is a possibility that it will rain, so it's a good idea to take an umbrella.
• In case + 'of'
  
  In case of means 'if there is'.
  
  
  • In case of emergency, call this number.
    = If there is an emergency, call this number.
• Unless
  
  Unless means 'except if' or 'only if'.
  Unless replaces 'if' + a negative verb.
  
  
  • Sally won't come unless you invite Harry.
    • Sally won't come except if you invite Harry.
    • Sally will only come if you invite Harry.
    • If you don't invite Harry, Sally won't come.
  • We will have a picnic unless it rains.
    • We will have a picnic except if it rains.
    • If it doesn't rain we will have a picnic.
    • If it rains, we won't have a picnic.