Conditional execution. If the matching If command and all preceding matching ElseIf commands fail (their expressions evaluate to 0) and if expression is nonzero, subsequent commands until the next matching ElseIf, Else, or EndIf are executed.
Syntax
ElseIf expression [Then]
The Then keyword is optional.
Example
IF PLANE_ALT > 3000 THEN
PRINT "Altitude is greater than 3,000."
ELSEIF PLANE_ALT > 2000 THEN
PRINT "Altitude is greater than 2,000."
ELSEIF PLANE_ALT > 1000
PRINT "Altitude is greater than 1,000."
ELSE
PRINT "Altitude is less than 1,001."
ENDIF