Introduction to BASIC
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.