CASE ~ WHEN ~ OTHERWISE ~ ENDCASE

A CASE block allows you to choose a section of code to run based on a value or result of an expression. This control structure is often called a switch statement in other languages.

Syntax

CASE caseVal
 WHEN whenVal1
  whenBody1...
{WHEN whenVal2
  whenBody2...}...
{OTHERWISE
  otherwiseBody...}
ENDCASE

Examples

A CASE block can contain any number of WHEN sections. These sections are checked in order to see if they match the CASE, and the first match is run.

VAR I%
PRINT "1) Cake"
PRINT "2) Burger"
PRINT "3) Salad"
INPUT "Choice";I%
PRINT "You chose: ";
CASE I%
 WHEN 1
  PRINT "Cake"
 WHEN 2
  PRINT "Burger"
 WHEN 3
  PRINT "Salad"
ENDCASE

If two WHEN sections have the same value, then the first one is used; the second will never be reached.

INPUT I
CASE I
 WHEN 1
  PRINT "one"
 WHEN 2
  PRINT "two"
 WHEN 1
  PRINT "you'll never meet me!"
ENDCASE

If no WHEN sections are matched, then the OTHERWISE section is matched, if it is present.

CASE RND(100)
 WHEN 7
  PRINT "Lucky!"
 WHEN 13
  PRINT "Unlucky..."
 OTHERWISE
  PRINT "Just a number."
ENDCASE

To match multiple values to one block, just use two WHEN statements next to each other.

VAR I
INPUT I
CASE I
 '1 and 2 match the same block
 WHEN 1
 WHEN 2
  PRINT "One or two"
 'this way also works
 WHEN 3:WHEN 4
  PRINT "Three or four"
ENDCASE

Keep in mind that this means you cannot write a WHEN block that does absolutely nothing, unless it is last in the CASE. If a WHEN block is empty, it just matches to the one below it. To match a value and then do nothing, you'll have to write some code in the block that does nothing, or write it last.

CASE I
 WHEN 2
  PRINT "two"
 'we want 1 to do nothing
 WHEN 1
ENDCASE

Also note that, since matches are evaluated in order, if this CASE contains an OTHERWISE you cannot rely on writing the "ignored" match last. You will have to resort to writing meaningless code in the matches you want to explicitly ignore

CASE I
 WHEN 1
  'this does nothing
  NOP
 WHEN 2
  PRINT "two"
 OTHERWISE
  PRINT "another number"
ENDCASE
'this function does nothing
DEF NOP END

If an empty WHEN is written before an OTHERWISE, then that value is simply matched to OTHERWISE.

CASE I
 WHEN 2
  PRINT "two"
 WHEN 1
 OTHERWISE
  PRINT "another number"
ENDCASE

---

The OTHERWISE section can be placed anywhere within the CASE block, but it is standard to put it at the end, because matches are evaluated in order. If OTHERWISE is written first, for example, then it will always match.

'OTHERWISE will be matched, even if 7 or 13 are entered!
CASE RND(100)
 OTHERWISE
  PRINT "Just a number."
 WHEN 7
  PRINT "Lucky!"
 WHEN 13
  PRINT "Unlucky..."
ENDCASE

If multiple OTHERWISE blocks are written, then they are all checked in order and will all match. This can be confusing, so it's recommended to just use one.

'you shouldn't do this!
'OTHERWISE will be matched if 13 is entered, but not 7, due to order
CASE RND(100)
 WHEN 7
  PRINT "Lucky!"
 OTHERWISE
  PRINT "Just a number."
 WHEN 13
  PRINT "Unlucky..."
 OTHERWISE
  PRINT "Still just a number."
ENDCASE

Using multiple OTHERWISE blocks or placing them anywhere other than last can cause unexpected behavior, so it should be avoided.

'just do this instead...
'OTHERWISE will only be matched if 7 or 13 are not matched
CASE RND(100)
 WHEN 7
  PRINT "Lucky!"
 WHEN 13
  PRINT "Unlucky..."
 OTHERWISE
  PRINT "Just a number."
  PRINT "Still just a number."
ENDCASE

An empty OTHERWISE cannot be written before a WHEN. This is a syntax error.

CASE I
 WHEN 2
  PRINT "two"
 OTHERWISE  '<--- syntax error
 WHEN 1
  PRINT "one"
ENDCASE

Notes

Fallthrough

In some languages, matches will "fall through" one another unless the associated block doesn't contain a break. There is no fallthrough feature in SmileBASIC, so a BREAK is unnecessary.

Exit Behavior: WHEN vs OTHERWISE

After a WHEN is matched, the interpreter stops checking for further WHEN matches and exits the CASE block. However, after OTHERWISE is matched, the interpreter keeps looking for possible matches. This is what allows there to be multiple OTHERWISE blocks, and in any order, while also meaning that only one WHEN of a specific value will be matched. This also means that whether or not OTHERWISE will be matched is dependent on the order of the matches, and that a WHEN can be matched after an OTHERWISE. In this example, if I is 1, no OTHERWISE blocks are matched. If I is 2, only the first is matched, and then WHEN 2 is matched. If I is any other value, both are matched.

CASE I
 WHEN 1
  PRINT "One"
 OTHERWISE
  PRINT "Otherwise A"
 WHEN 2
  PRINT "Two"
 OTHERWISE
  PRINT "Otherwise B"
ENDCASE