Introduction to BASIC   Exception Handling

WHEN ~ END WHEN
Errors that occur on execution are called exceptions.
Division by zero or overflow is an example of an exception.
Exception handling enables continuation of a program when an exception has occurred.


Example. The graph of the function y=1/x

10 SET WINDOW -4,4,-4,4
20 FOR x=-4 TO 4 STEP 0.01
30    WHEN EXCEPTION IN
40         PLOT LINES: x,1/x;
50    USE
60         PLOT LINES
70    END WHEN
80 NEXT x
90 END



The statements written between the USE line and the END-USE line are not executed ordinarily.
If an exception has occurred in a statement written between the WHEN-EXCETION-IN line and the USE line, the control shall be switched to the next line of the USE line.
A PLOT LINES statement with no arguments disconnects the continuation of segments.

Refer to Execption Handling