ON ERROR
========

Function
--------

ON ERROR is used to catch errors which would normally give a Basic Error
message.

Syntax
------

ON ERROR GOTO [line no]

ON ERROR GOTO 0

Examples
--------

::

   10 ON ERROR GOTO 1000
   20 INPUT A
   30 A = SQR(A)
   40 PRINT A
   50 GOTO 20
   1000 A=ABS(A)
   1010 PRINT "NEGATIVE NUMBER CORRECTED"
   1020 RESUME 30

This example will trap negative numbers and correct the condition.

Remarks
-------

ON ERROR causes program execution to be diverted to an error handling
subroutine.

Any error can be trapped. However, ON ERROR is normally used for
correctable errors, e.g. magnitude errors, which could be caused by
operator input etc.

An ON ERROR trap must be exited by either an :doc:`resume`
statement or by ON ERROR GOTO 0 which will give the normal Basic error
message.