5. SWITCH / CASE statement

You have seen how the IF statement allows you to test whether an instruction should run. It is a very common requirement that you want to test for a set of values rather than just a single one.

The long way of doing this is to write

if (x = 'Monday') then ....

if (x = 'Tuesday)' then ....

if (x = 'Wednesday') then ...

and so on. This works but it seems to take an awful lot of source code.

What you need is a SWITCH construct. The purpose of a switch statement is to test the condition only once then branch to one of a set of choices.

Unfortunately every language seems to have a very different way of laying out a switch statement but the pseudo-code for the general idea is shown below

  SWITCH x
  	
     CASE 'Monday': Print ()
     CASE 'Tuesday': Work_salary()
     default: Store()
  END    
  

It begins with a test for the condition of x, which is the SWITCH part. Then the appropriate CASE is run depending on the value of x. In this case it will handle x being Monday or Tuesday. Should x be neither of those values then the DEFAULT statement is run. You can of course have more than two cases and you can have many statements within each case block.

As I say, every language seems to implement this in a different way. For instance

'C' language

  switch (x){
    case 'monday':
    	Print ();
        break;
    case 'tuesday':
    	Work_salary()
        break;
    default:
       Store();
    	break;		        
  }
  

C insists on having a 'break' statement to stop the next case also being run.

Perl language

(another popular web server language) it looks like

  use feature 'switch'
    given (x) {
  	when ("monday") {
    	Print ();
    }
  	when ("tuesday") {
    	Work_salary()
    }
    default:
       Store();
  }		        
  

In this language the CASE statement become 'when'.

But the essential element is that there is a method to test the state of a variable then jumping to one of a set of statement blocks. You can write an algorithm in pseudo-code which may then be coded in any number of different languages.