IF condition THEN statement [ : statement ... ] 
   [ ELSE statement [ : statement ... ]]
   
IF condition THEN expression [ ELSE expression ]

IF condition THEN
   statement
   statement
ELSE IF condition THEN
   statement
ELSE
   statement
END IF

   Synopsis:
      Tests the truth of a conditional expression

   Notes:
      IF..THEN tests whether a condition is true and decides which statement (or
         group of statements) to execute as a result.
      IF..THEN and IF..THEN..ELSE statements can occur either on a single line,
         or spread across multiple lines in a code block terminating with an
         END IF statement.
      In scripts with line numbers, these statements are interchangeable:
         10 IF number > 1 THEN GOTO 100
         10 IF number > 1 THEN 100
      If non-conditional expressions are used, they must evaluate to line 
         numbers or an error will occur. Complex expressions like '(x + 10) / 2' 
         can be used as well as simple line numbers like 100.

   Availability:
      Multiple-line IF..END IF code blocks aren't available in scripts with
         primitive line numbers.

   Examples
      IF number > 1 THEN PRINT "It is true!"
      IF number > 1 THEN PRINT "It is true!" : PRINT "This is also printed!"
      IF number > 1 THEN PRINT "It is true!" ELSE PRINT "It is false!"

      IF number > 100 THEN
         PRINT "Greater than 100!"
      ELSE IF number < 5 THEN
         PRINT "Less than 5!"
      ELSE
         PRINT "Number is between 5 and 100"
      END IF

      10 LET number = 5
      20 IF number > 10 THEN 100
      30 IF number > 1 THEN 200 ELSE 300
      100 PRINT "Greater than 10"
      110 STOP
      200 PRINT "Between 2 and 10"
      210 STOP
      300 PRINT "Less than 2"
      310 END
