The switch-Statement

1. Another way to implement multiway branches is to use a switch-statement.
   
   
2. The syntax of the switch-statement is:
   
   switch (Controlling_Expression)
       {
           case const_1:
               Statement_Sequence_1
           case const_2:
               Statement_Sequence_2
   .
   .
   .
           case const_n:
               Statement_Sequence_n
           default:
               Default_Statement_Sequence
       }
   
   
   • The controlling expression is first evaluated. It must return a bool, an integer, a character, or a enum type.
     
   • The constant values given after the various occurrence of the keyword case is checked one by one until a match is found with the value of the controlling expression.
     
   • The sequence of statements for that case are then executed.
     
   • Often each of the statement sequence ends with a break statement. When a break statement is encountered, the switch-statement ends.
     
   • Execution will fall through to the next case if a break statement is not found at the end of a statement sequence.
     
   • The default case is optional. The statements associated with it are executed if there is no match with any of the other cases.
     
     
3. //Program to illustrate the switch-statement.
   #include <iostream>
   using namespace std;
   
   int main( )
   {
       char grade;
   
       cout << "Enter your midterm grade and press return: ";
       cin >> grade;
   
       switch (grade)
       {
           case 'A':
               cout << "Excellent. "
                       << "You need not take the final.\n";
               break;
           case 'B':
               cout << "Very good.\n";
               cout << "Good luck on the final exam. "
               break;
           case 'C':
               cout << "You are passing the course.\n";
               break;
           case 'D':
           case 'F':
               cout << "Not good. "
                       << "Go study.\n";
               break;
           default:
               cout << "That is not a possible grade.\n"
                   << "Are you trying to trick me?\n";
       }
   
       cout << "End of program.\n";
       return 0;
   }
   
   
4. A menu in a computer program presents a list of alternatives on the screen for the use to choose from. The switch-statement is often used for implementing a menu.
   
   
5. Go back to this example after we have dealt with functions.
   //Program to give out homework assignment information.
   #include <iostream>
   using namespace std;
   
   void show_assignment( );
   //Displays next assignment on screen.
   
   void show_grade( );
   //Asks for a student number and gives the corresponding grade.
   
   void give_hints( );
   //Displays a hint for the current assignment.
   int main( )
   {
       int choice;
   
       do
       {
           cout << endl
                   << "Choose 1 to see the next homework assignment.\n"
                   << "Choose 2 for your grade on the last assignment.\n"
                   << "Choose 3 for assignment hints.\n"
                   << "Choose 4 to exit this program.\n"
                   << "Enter your choice and press return: ";
           cin >> choice;
   
           switch (choice)
           {
               case 1:
                   show_assignment( );
                   break;
               case 2:
                   show_grade( );
                   break;
               case 3:
                   give_hints( );
                   break;
               case 4:
                   cout << "End of Program.\n";
                   break;
               default:
                   cout << "Not a valid choice.\n"
                       << "Choose again.\n";
           }
       } while (choice != 4);
   
       return 0;
   }
   
   void show_assignment( )
   {
       cout << endl << "show_assignment not implemented.\n";
   }
   
   void show_grade( )
   {
       cout << endl << "show_grade not implemented.\n";
   }
   
   void give_hints( )
   {
       cout << endl
               << "Assignment hints:\n"
               <<"Analyze the problem\n"
               << "Write an algorithm in pseudocode.\n"
               << "Translate the pseudocode into a C++ program.\n";
   }