The Switch Statement

• This is from chapter 7, section 1
• It is a continuation of selection, so I will cover it here.
• This is ONLY for enumerable types
  • A type is enumerable if each potential value has a known predecessor and successor.
  • Integer types qualify
  • enum (which is the first thing in 230) qualifies
  • Strings, floats, and most other data types do not qualify.
• Syntax is somewhat complex
  • switch (enumerable expression) { }
  • Inside the code block is a series of case statements
  • case value: [statements;] (the statement is optional)
  • or default: statements;
• The case values must be constants.
• A syntax error is generated if two cases are identical.
• Semantics
  • Evaluate the enumerable expression
  • Find the corresponding case and execute through the end of the code block
  • If no corresponding case exists, and the default case does, execute statements starting with default.
• This is really not the desired behavior, so we use the break statement.
  • The break statement exits the innermost control structure.
  • You may only use the break statement in switch statements for your stay here at Edinboro.
  • DO NOT USE BREAK TO EXIT
    • if, if-else
    • loops of any type
• A switch example:
  • Write a simple adventure game. The user is in a field, to the north is a nasty bear, to the east a lion, to the south an alligator and to the west a nice sunset with the partner of their choice. Ask the user for a single character, the direction they wish to travel. Accept the following

    Key	Direction
    N, w, k	North
    S, s, j	South
    E, a, h	East
    W, d, l	West

  • A simple implementation
  • How will I test this code?
    • I will play all 12 letters to make sure that they work.
    • I will try some other characters as well.
• Should you use the switch statement
  • I believe you should for several reasons
  • It is easier to modify than if - else if - else ...
  • It checks for duplicate case, thus preventing errors.