Switch Statements

• This is from page 304 of the book.
  • But be cautioned, it has been added to
  • reference.
  • (I think this is the first time I saw a c++23 change in a man page)
• The switch statement is a control structure we did not cover last semester.
  • It is a more structured way to do an if-else if- else if ... statement.
  • It is for cases like our enum
  • It is only for enumerable types, or types that can be mapped to the integers.
• Syntax

  • switch (expression)  {
        case constvalue: 
            expressions;
            [break;]
        case constvalue:
            expressions;
            [break;]
        default:
            expressions;
    } 

  • the constvalue values must all be different.
  • expressions; are not required. Multiple case statements can be adjacent.
  • break; is optional
    • if not present, flow of control will fall through to the next case statement.
  • The default statement is optional but usually important.
• Semantics
  • The expression is evaluated
  • If it matches a case statement, the expressions following that are executed.
  • If it does not match any case statement, and default is present, the statements following the default statement are executed.
  • If a break is encountered, execution is transferred outside of the switch statement.
• Example:

  string SizeTToString(SizeT size){
      string name{"unknown"};
  
      switch(size)  {
          case SizeT::TINY:
              name = "tiny";
              break;
          case SizeT::SMALL:
              name = "small";
              break;
          case SizeT::MEDIUM:
              name = "medium";
              break;
          case SizeT::LARGE:
              name = "large";
              break;
          case SizeT::HUGE:
              name = "huge";
              break;
          case SizeT::GARGANTUAN:
              name = "gargantuan";
              break;
          default:
              cout << "Error, unknown size" << endl;
      }
      

• A word on break.
  • It transfers control out of the closest enclosing loop or switch statement.
  • We ONLY use it in switch statements at PW:E
• There are two other forbidden statements
  • We do not use goto
  • We do not use continue
• And return
  • For now is only used as the last statement of a function.
• Fallthrough
  • Consider code to generate the comment a Huge creature might make.

    string HugeComment(SizeT size){
        string response;
        switch(size)  {
            case SizeT::TINY:
            case SizeT::SMALL:
            case SizeT::GARGANTUAN:
                response = "What, I don't see you!";
                break;
            case SizeT::MEDIUM:
                response = "Look at that tiny little thing!";
                break;
            case SizeT::LARGE:
                response = "Will you be my friend?";
                break;
            case SizeT::HUGE:
                response = "Look at that big thing!";
                break;
            default:
                response = "I don't know what size that thing is!";
         }
         return response;
    }
        

• Take a look at, or write simpleGame2.cpp