Making decisions

IF

A block IF has no THEN. It ends with END IF.

hp = 35

IF hp > 50
    PRINT "fine"
ELSE IF hp > 0
    PRINT "hurt"
ELSE
    PRINT "down"
END IF

hurt

THEN is for when the whole thing fits on one line. That form has no END, and it can have an ELSE on the end — even ELSE IF, if you can stand the length.

hp = 0
IF hp = 0 THEN PRINT "game over"
IF hp > 0 THEN PRINT "you won't see this"

IF hp > 50 THEN PRINT "fine" ELSE PRINT "not fine"
IF hp > 50 THEN mood = "happy" ELSE IF hp > 0 THEN mood = "worried" ELSE mood = "napping"
PRINT mood

game over
not fine
napping

Each side takes one statement. When you need two, that’s what the block form is for.

From BASIC: A block IF doesn’t end its first line with THEN, and it’s ELSE IF, two words. (If you’ve got a lot of old code, the last lesson shows a way to let me read it as it is.)

From Python: ELSE IF is your elif. No colons.

From JavaScript: No parentheses needed around the condition, and no braces around the block.

From Lua: ELSE IF is your elseif, and there’s no then on a block.

SELECT CASE

When you’re asking what one value is, SELECT CASE reads better than a ladder of ELSE IF. I work the value out once, then run the lines under the first CASE that fits — only that one.

score = 95

SELECT CASE score
    CASE 100
        PRINT "perfect!"
    CASE 90 TO 99
        PRINT "great"
    CASE 50, 60, 70, 80
        PRINT "a round number"
    CASE IS < 50
        PRINT "oops"
    CASE ELSE
        PRINT "fine"
END SELECT

great

A CASE can list values with commas, give a range with TO, or compare with IS. CASE ELSE catches everything and goes last. Change score over there and see which one I pick.

From Python: This is your match, for values.

From JavaScript: This is your switch, without the break. A case never falls through into the next.

From Lua: You never had one of these. Enjoy!