IF statement( IF line) ☆☆
IF logical_expression THEN imperative_statement
IF logical_expression THEN imperative_statement1 ELSE imperative_statement2
IF D>0 THEN PRINT (-b+sqr(D))/(2*a),(-b-sqr(D))/(2*a)
IF A=1 THEN PRINT "Y" ELSE PRINT "N"
Only one imperative statement can be written succeeding THEN and only one imperative statement can be written succeeding ELSE (if any).
An imperative statement is a statement that is neither declarative nor part of a block.
Many statements such as LET, PRINT, INPUT, SET, PLOT, GOTO, EXIT, CALL, STOP are imperative, but a IF statement is not imperative.
Thus, no IF statement can be written succeeding THEN.
Therefore, Full BASIC never generate an obscure statement like
IF a=0 THEN IF b=1 THEN … ELSE …
An IF-line that has no statement succeeding THEN is regarded as part of an IF～END IF block, and consequently a corresponding END-IF-line is needed.