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Euphoria - Switch Statements

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The switch Statement:

The switch statement is used to run a specific set of statements, depending on the value of an expression. It often replaces a set of if-elsif statements giving you more control and readability of your program.

Syntax:

The syntax of simple switch statement is:

switch expression do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
   .....................
   case else
      -- Executes when the expression does not matches any case.  
end if

The <val> in a case must be either an atom, literal string, constant or enum. Multiple values for a single case can be specified by separating the values by commas. By default, control flows to the end of the switch block when the next case is encountered.

Example:

#!/home/euphoria-4.0b2/bin/eui

atom marks = 'C'

switch marks do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

This would produce following result:

Well done!

The switch...with fallthru Statement:

The case statement of a switch is executed when it matches with the given expression value and by default it comes out. By default, control flows to the end of the switch block when the next case is encountered.

The default for a particular switch block can be changed so that control passes to the next executable statement whenever a new case is encountered by using with fallthru in the switch statement:

Syntax:

The syntax of simple switch...with fallthru statement is:

switch expression with fallthru do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
      break -- optional to come out of the switch from this point.
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
      break -- Optional to come out of the switch from this point.
   .....................
   case else
      -- Executes when the expression does not matches any case.  
      break -- Optional to come out of the switch from this point.
end if

Example:

#!/home/euphoria-4.0b2/bin/eui

atom marks = 'C'

switch marks with fallthru do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

This would produce following result:

Well done!
You passed!
Better try again!
Invalid grade!

You can use optional break statement to come out from a point inside a switch statement as follows:

#!/home/euphoria-4.0b2/bin/eui

atom marks = 'C'

switch marks with fallthru do
   case 'A' then
      puts(1, "Excellent!\n" )
      break
   case 'B', 'C' then
      puts(1, "Well done!\n" )
      break
   case 'D' then
      puts(1, "You passed!\n" )
      break
   case 'F' then
      puts(1, "Better try again!\n" )
      break
   case else
      puts(1, "Invalid grade!\n" )
      break
end switch

This would produce following result:

Well done!

The switch....label Statement:

The switch statement can have an optional label to name the switch block. This name can be used in nested switch break statements to break out of an enclosing switch rather than just the owning switch.

A switch lable is used just to name the block and label names must be double quoted constant strings having single or multiple words. The label keyword is a case sensitive and should be written as label.

Syntax:

The syntax of simple switch...label statement is:

switch expression label "Label Name" do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values
      break "LEBEL NAME" 
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values 
      break "LEBEL NAME"  
   .....................
   case else
      -- Executes when the expression does not matches any case.
      break "LEBEL NAME"   
end if

Example:

#!/home/euphoria-4.0b2/bin/eui

atom marks = 'C'
atom scale = 'L'

switch marks label "MARKS" do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
      switch scale label "SCALE" do
         case 'U' then
             puts(1, "Upper scale!\n" )
             break "MARKS"
         case 'L' then
             puts(1, "Lower scale!\n" )
             break "MARKS"
         case else
             puts(1, "Invalid scale!\n" )
             break "MARKS"
      end switch
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

This would produce following result:

Well done!
Lower scale!

Note: If you are not using a with fallthru statement then you do not need to use a lable because switch statement would come out automatically.


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