QBasic 1.1: ON ERROR Statement

Explanation

ON ERROR Statement

Enables error handling and, when a run-time error occurs, directs your program to either branch to an error-handling routine or resume execution.

Worth knowing

Useful and cross-version information about the programming environments of QBasic, QuickBasic and Visual Basic for DOS.

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You are here: References Overview > QBasic 1.1 Commands List > ON ERROR Statement

Syntax

ON ERROR {GOTO line | RESUME NEXT}

Description / Parameter(s)

GOTO line	Branches to the first line of the error-handling routine, specified by a label or line number. To disable error handling, specify GOTO 0.
RESUME NEXT	Resumes execution with the statement following the statement that caused the run-time error. Use the ERR function to obtain the error code for the error.
If ON ERROR isn't used, any run-time error ends your program.

Example


'Illustrates ERDEV, ERDEV$, ERL, ERR, ERROR, ON ERROR, and RESUME.
   ON ERROR GOTO Handler
10 CHDIR "a:\"                'Causes ERR 71 "Disk not ready"
                              'if no disk in Drive A.
20 y% = 0
30 x% = 5 / y%                'ERR 11 "Division by zero."
40 PRINT "x% ="; x%
50 ERROR 57                   'ERR 57 "Device I/O error."
 
Handler:
  PRINT
  PRINT "Error "; ERR; " on line "; ERL
  SELECT CASE ERR
    CASE 71
      PRINT "Using device "; ERDEV$; " device error code = "; ERDEV
      RESUME NEXT
    CASE 11
      INPUT "What value do you want to divide by"; y%
      RESUME                  'Retry line 30 with new value of y%.
    CASE ELSE
      PRINT "Unexpected error, ending program."
      END
  END SELECT