Transfers control to an internal subroutine determined by the current value of a given expression.
ON expression GOSUB statement-label{,statement-label}...
expression is any DataBasic expression that evaluates to an integer value.
statement-label is the label of the statement where control is to be transferred. It is any numeric or alphanumeric label.
The ON GOSUB statement evaluates expression, which must evaluate to an integer. If expression evaluates to 1, control is transferred to the first statement label. If expression evaluates to 2, control is transferred to the second statement label, and so on.
If expression evaluates to less than one, the following message is displayed and the branch is taken to the first statement label:
[B22] BRANCH INDEX OF x IS ILLEGAL;
BRANCH TAKEN TO FIRST STATEMENT-LABEL!
If expression evaluates to an integer greater than the number of statement labels in the list, the following message is displayed and the branch is taken to the last statement label:
[B23] BRANCH INDEX OF x EXCEEDS NUMBER OF STATEMENT-LABELS;
BRANCH TAKEN TO LAST STATEMENT-LABEL!
If any of the statement labels in the list refers to a label that does not exist, the program will not compile and an error message is printed.
The RETURN statement returns control to the statement immediately following the ON GOSUB statement that called the subroutine.
The RETURN TO statement returns control to a specific statement specified by statement-label.
ON GOTO statement, GOSUB statement, MultiValue Compatibilty.
ON X+Y GOSUB 101, 117, 103, 216 PRINT Y
Transfers control to the internal subroutine with statement label 101, 117, 103 or 216, depending on whether the value of X+Y is 1 (or less than 1), 2, 3 or 4 (or more than 4). Y is printed when control returns from the subroutines.
ON Z GOSUB 20, 20, 29 INPUT A
Transfers control to label 20 if Z <= 2, or to label 29 in all other cases. The system prompts for input when control returns via a RETURN statement.
IF T GE 1 AND T LE 3 THEN ON T GOSUB 110, 120, 130 END
The IF statement guarantees that T is in the range of the computed GOSUB statement, so that a 'branch index' message is not displayed.