(1) An IF ~ END IF block can contain an ELSEIF line.
IF logical_exp1 THEN ………1 ELSEIF logical_exp2 THEN ………2 ELSE ………3 END IF
is equivalent to
IF logical_exp1 THEN ………1 ELSE IF logical_exp2 THEN ………2 ELSE ………3 END IF END IF
If logical_exp1 is true, ………1 shall be executed, otherwise logical_exp2 is true, ………2 shall be executed, otherwise ………3 shall be executed.
Example.
! Solve a quadratic equation INPUT a, b, c LET D=b^2-4*a*c IF D>0 THEN PRINT (-b+sqr(D))/(2*a),(-b-sqr(D))/(2*a) ELSEIF D=0 THEN PRINT -b/(2*a) ELSE PRINT "no solution" END IF END
(2) An IF~END IF block can contain more than one ELSEIF line.
IF logical_exp1 THEN
………1
ELSEIF logical_exp2 THEN
………2
ELSEIF logical_exp3 THEN
………3
~~~
~~~
ELSEIF logical_expn-1 THEN
………n-1
ELSE
………n
END IF