Vector Basic Interpreter Basic 80 Reference Manual - page 60
IF
THEN
number> [ELSE I number>] IF GOTO number> [ELSE I number>] SK, Ex~ended, Disk The ELSE clause is allowed only in Extended' and Disk versions. To make a decision regarding program flow based on the result returned by an expression. If the result of is not zero, the THEN or GOTO clause is executed. THEN may be followed by either a line number for branching or one or more statements to be executed. GOTO is always followed by a line number. If the result of is zero, the THEN or GOTO clause is ignored and the ELSE clause, if present, is executed. Execution continues with the nex~ executable statement. (ELSE is allowed only in Ex~ended and Disk versions.) Extended and Disk versions allow a comma before THEN. Nes~inq 2! B:. Statements In the E~ended and Disk versions, IF •••THEN •••ELSE statements may be nested. Nes~ing is limited only by the length of the line. For example IF X>Y THEN PRINT IIGREATERIIELSE IF Y>X THEN PRINT llLESS THAN IIELSE PRINT •• EQUAL" is a legal statement. If the statement does not contain the same number of ELSE and THEN clauses, each ELSE is matched with the closest unmatched THEN. For example IF A=B THEN IF a=c THEN PRINT II A-C II ELSE PRINT IIAOC" will not print "A<>CII when A<>B. If an IF •••THEN statement is followed by a number in the direct mode, an IIUndefined error results unless a statement with specified line number had previously entered in the indirect mode. line line II the been