#178 – Throwing an Exception from a switch Statement

December 12, 2010 2 Comments

Instead of a break statement as a terminator of a case clause in a switch statement, you can also throw an exception.

            switch (surname)       // surname is a string
            {
                case "Aarhus":
                case "Enevoldsen":
                    Console.WriteLine("Norwegian");
                    break;
                case "Brosnan":
                case "McGill":
                    Console.WriteLine("Irish");
                    throw new ApplicationException("Software doesn't work for Irish people");
                default:
                    Console.WriteLine("UNKNOWN origin");
                    break;
            }

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#177 – Using goto in a switch Statement

December 11, 2010 Leave a comment

You can use a goto statement within a switch statement to jump to another case clause.  This allows you to execute the contents of more than one case clause for a particular value of the switch expression.

            switch (day)
            {
                case DayOfWeek.Sunday:
                    Console.WriteLine("Go to church");
                    goto case DayOfWeek.Saturday;
                case DayOfWeek.Monday:
                    Console.WriteLine("Read Ulysses");
                    break;
                case DayOfWeek.Tuesday:
                    Console.WriteLine("Call Dad");
                    goto case DayOfWeek.Saturday;
                case DayOfWeek.Wednesday:
                    Console.WriteLine("Do laundry");
                    goto case DayOfWeek.Thursday;
                case DayOfWeek.Thursday:
                    Console.WriteLine("Watch a movie");
                    break;
                case DayOfWeek.Friday:
                    Console.WriteLine("Take out the trash");
                    goto case DayOfWeek.Tuesday;
                case DayOfWeek.Saturday:
                    Console.WriteLine("Relax");
                    break;
            }

This results in the following output:

  • Sunday: Go to church; Relax
  • Monday: Read Ulysses
  • Tuesday: Call Dad; Relax
  • Wednesday: Do laundry; Watch a movie
  • Thursday: Watch a movie
  • Friday: Take out the trash; Call Dad; Relax
  • Saturday: Relax

Think carefully before using goto in a switch statement.  There are often more clear ways to implement the same logic.

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#176 – Switch Statement Doesn’t Fall Through from Case to Case

December 10, 2010 1 Comment

Unlike C++, in C# you can’t force execution of a switch statement to “fall through” from one case clause to another by leaving out the break statement.  Each case clause must end with a break, goto, throw or return statement.

The following code results in a compile-time error.

            switch (carType)    // carType is a string
            {
                case "Saturn":
                    Console.WriteLine("Domestic car");
                case "Yugo":
                    Console.WriteLine("Inexpensive car");
                    break;
            }

Technically, the requirement is that the end of the statement block in a case clause must not be reachable–implying that you must transfer control out of the block, typically with a break statement.  This requirement means that it would be valid syntax to include an infinite loop in a case clause, without a break statement.

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#175 – The default Clause of a switch Statement

December 9, 2010 Leave a comment

Normally, if the value of the expression in a switch statement doesn’t match any of the values listed in the case clauses, control falls through the switch statement and none of the clauses are executed.

Optionally, you can provide a default clause, which will get executed if none of the case clauses are satisfied.

            switch (surname)       // surname is a string
            {
                case "Aarhus":
                case "Enevoldsen":
                    Console.WriteLine("Norwegian");
                    break;
                case "Brosnan":
                case "McGill":
                    Console.WriteLine("Irish");
                    break;
                case "Afonso":
                case "Silva":
                    Console.WriteLine("Portuguese");
                    break;
                default:
                    Console.WriteLine("UNKNOWN origin");
                    break;
            }

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#174 – Multiple Case Statements in switch Statement Can Share Code

December 8, 2010 Leave a comment

In a C# switch statement, you can group several case statements with the same block of code.  If the switch expression has a value matching any of the listed case statements, the corresponding code will be executed.

            switch (movieRating)    // 1-5
            {
                case 1:
                case 2:
                    Console.WriteLine("Not worth seeing");
                    break;
                case 3:
                case 4:
                    Console.WriteLine("Consider seeing it");
                    break;
                case 5:
                    Console.WriteLine("Absolutely must see it");
                    break;
            }

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#173 – The switch Statement

December 7, 2010 2 Comments

Use the switch statement in C# to execute one of several different blocks of code based on the possible values of a single expression.

            // 1 = Easy, 2 = Normal, 3 = Hard
            uint gameDifficulty = GetDifficulty();

            uint score = GetScore();
            uint totalScore;

            switch (gameDifficulty)
            {
                case 1:
                    Console.WriteLine("This is an EASY game");
                    totalScore = score / 2;
                    break;
                case 2:
                    Console.WriteLine("This is a NORMAL game");
                    totalScore = score;
                    break;
                case 3:
                    Console.WriteLine("This is a HARD game");
                    totalScore = score * 2;
                    break;
            }

The type of the expression must be one of the built-in primitive value types, a string or an enum.

The expression is evaluated and if the resulting value is listed as a value in one of the case clauses, the statements within that case are executed.

Each case clause must be terminated with some sort of jump statement.  The break statement is typically used, which causes control to jump to the next statement following the switch statement.

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