ERROR simulates a Basic error with the advantage that it allows user defined codes. For a list of Basic error messages, see Errors And Warnings.
10 INPUT a,b 20 ON ERROR GOT0 100 30 IF a>b THEN ERROR 156 40 GOTO 10 100 IF ERR = 156 THEN PRINT "a>b error" 110 RESUME 10
The ERROR statement neatly traps errors and forces the printing of a Basic error message. If the error number is undefined in Basic, then processing can be forced to restart at another line to print a user defined message. When ERROR is set to n, this number may be recovered with ERR, and the line number with ERL.
After a forced user error trap, a suitable RESUME command must be executed to ensure correct program operation.